This glossary is not in alphabetical order. Rather, the most basic concepts appear before harder ones. The information builds on itself.

Types of On-Yomi

types of on-yomi: The Japanese didn't import kanji in one fell swoop. Rather, as migrants, students, tourists, envoys, and priests moved between Korea, China, and Japan, people introduced Chinese characters to Japan. The characters originated in different parts of China, and pronunciations of each character often varied regionally. As dynasties changed, so did rulers' dialects, which also altered the sounds of characters. For that reason, one character may now have several on-yomi. The Japanese classify these readings according to the era in which they originated in China (which is not the same as the era in which the characters entered Japan). It's hard to say exactly when each kind of yomi originated because sources differ. To keep things really simple, I've settled on a range of dates. Here's how this plays out for 行 (to go):

呉音 (ごおん, from Chinese
readings of the 5th–6th c.): ギョウ
EXAMPLE: 行事 (ぎょうじ: event)
漢音 (かんおん, from Chinese
readings of the 7th–8th c.): コウ
EXAMPLE: 銀行 (ぎんこう: bank)
唐音 (とうおん, from Chinese
readings of the 12th c. and onward):
EXAMPLE: 行脚 (あんぎゃ: pilgrimage, travel on foot)

If the three yomi differ, you'll find them all listed in the Character Profile of Joy o' Kanji. However, if the yomi has not changed over the years, you'll see only a 呉音 listing. Sometimes you'll find entries for 呉音 and 漢音 but not for 唐音. As if all that weren't enough to digest, there's a fourth classification. When an on-yomi doesn't belong to any of the three types above, the Japanese call that yomi 慣用音 (かんようおん), which translates as "traditional (popularly accepted) pronunciation (e.g., of a kanji)." For example, here are the on-yomi for 茶 (tea):

呉音: ジャ、ヂャ                                        
唐音: EXAMPLE: 喫茶店 (きっさてん: café)
慣用音: チャ EXAMPLE: お茶 (おちゃ: green tea)

So many yomi to choose from (and all rhyming!), but no one uses ジャ, ヂャ, or タ anymore. The only relevant ones are サ and チャ.

I've been puzzled to find some 慣用音 that have fallen out of use. How can something be both popular and obsolete? The answer lies in a statement from the publisher of the dictionary Kojien. He says that 慣用音 just represents a reading that cannot be accounted for using the phonetic rules of 呉音, 漢音, or 唐音. Only some 慣用音 are popularly accepted, whereas others are not. Therefore, 慣用音 is a rather misleading term. Aha!

Further Reading: For more on the following topic, see these parts of Crazy for Kanji

types of on-yomi: page 36, column 2, and page 37, column 1

The Term Joyo

The name Joy o' Kanji is a play on the word Jōyō.

Jōyō (常用): Kanji that the Japanese Ministry of Education selected for regular use in 1981. The ministry determined that newspapers and magazines would limit their kanji to this pool of 1,945 characters, which schools would require students to know. However, the list changed in fall 2010 (officially going into effect in 2012), resulting in a set of 2,136 characters. Joy o' Kanji will cover all of them. As explained in "Note on Italicization" on the right, there won't be italics for the tools of the trade, so from now on, you won't see the word Jōyō italicized. Furthermore, this term will have no macrons (the horizontal lines indicating a long vowel). For the sake of simplicity, Joy o' Kanji largely does away with macrons.

Are all of these Joyo kanji? That might take awhile to determine!

The Japanese Scripts

Japanese text interweaves four scripts: kanji, hiragana, katakana, and romaji. Each script serves a separate function, so the Japanese rely on all of them when they write. A single sentence may include four scripts! Even a single word can combine scripts, as you'll see below in the example for the word romaji.

kanji (漢字): The most complicated-looking script used in Japanese writing. Almost all the characters in this script originated in China. The characters have both a sound and a meaning. EXAMPLE: 漢字, which says kanji. The first character, 漢, refers to China and is pronounced カン (KAN). The second character, 字, means "character" and is pronounced ジ (JI).

hiragana (平仮名): Loopy, cursive script used mainly for grammar (e.g., particles) but also for kanji that are too difficult to write. This script is phonetic; it represents the sounds in a word, but the actual strokes have no particular meaning. EXAMPLE: ひらがな, which says hiragana.

katakana (片仮名): Angular script used for words not of Japanese or Chinese origin. This script is phonetic; it represents the sounds in a word, but the actual strokes have no particular meaning. EXAMPLE: マクドナルド, which says Makudonarudo and means "McDonald's."

rōmaji (ローマ字): Romanized letters (the same ones used in the English alphabet) used to represent Japanese words. EXAMPLErōmaji is the romanized form of ローマ字, which combines katakana (ローマ) and kanji (字). From now on in Joy o' Kanji, you won't see the word rōmaji written as such. It will appear without a macron.

Putting It All Together: The following text combines all four scripts, with kanji in red, hiragana in blue, katakana in green, and romaji in black:

One writes 群馬 in romaji as Gunma.
群馬 (ぐんま: Gunma (Prefecture)); 字 (じ: character); 書く (かく: to write)

To derive full benefits from Joy o' Kanji, you'll need hiragana and katakana. In that spirit, the rest of this glossary will indicate the pronunciations of various kanji in those scripts, not in romaji.

Kana and Furigana

You may have noticed that 平仮名 (the kanji for hiragana) and 片仮名 (the kanji for katakana) look quite similar; only the first character differs. In each term, the last two kanji form an autonomous word, 仮名, pronounced as kana. Meanwhile, just as hiragana and kanji often combine in words and in sentences, the word furigana shows another way in which these two scripts relate to each other.

kana (仮名): Umbrella term for hiragana and katakana. Generally, people learn kana before kanji.

furigana (振り仮名): Small hiragana written under, above, or beside kanji, indicating their pronunciations. For a photo containing furigana, see essay 1095 (缶) or essay 1643 (倒).

The Pronunciation of Kanji: On-Yomi and Kun-Yomi

A yomi is the way to pronounce a character or word. There are generally two ways of reading characters—a “Japanese” way (a kun-yomi) and a “Chinese” way (an on-yomi). 

yomi (読み): Pronunciation of a character or word. Yomi roughly rhymes with “foamy.” Kanji often have scads of yomi, and each may have a distinct meaning.

on-yomi (音読み): Pronunciation of a character that roughly corresponds to the ancient Chinese pronunciation of that character. Some people call on-yomi Chinese readings, but this is somewhat misleading. When they were imported, Chinese pronunciations changed in Japanese mouths. Plus, over the millennia in both China and Japan, these sounds have evolved. On roughly rhymes with "bone" and means "sound." A character can have multiple on-yomi, just one, or none at all. ALSO CALLED: "on readings." 

Chinese teapot with a poem written in Chinese.

kun-yomi (訓読み): Pronunciation of a character that corresponds to the language spoken in Japan before kanji arrived. Kun rhymes with “noon” and means “teachings.” A character can have multiple kun-yomi, just one, or none at all. ALSO CALLED: "kun readings" or "Japanese readings." 

Putting It All Together: The kanji 山 (mountain) has two yomi: サン and やま. The use of katakana here indicates that サン is the on-yomi, whereas the use of hiragana indicates that やま is the kun-yomi. This convention is common in dictionaries and textbooks, and Joy o' Kanji has adopted this system.

Singletons, Compounds, and Voicing

Some characters stand by themselves, functioning as autonomous units. However, many other kanji bond with the characters at their sides. Identifying kanji as solitary or bonded can often give you clues about their yomi.

singleton (a term that Eve coined): Character standing alone, rather than being bonded to another kanji. EXAMPLE: 行 (い•く: to go) is a singleton, but that's no longer true when 行 is part of 旅行 (りょこう: travel). When you see a singleton, you’ll generally read it by using its kun-yomi. By the way, for an explanation of the raised dot in い•く, see the definition of okurigana below.

compound: Word consisting of two or more kanji. When you see a compound, you'll generally read it by using on-yomi. EXAMPLES: 電車 (でんしゃ: train); 大学院 (だいがくいん: graduate school). 

These are definitely functioning as singletons!

voicing (濁り, にごり): Slight changes that can happen to the yomi of a kanji if it is not in the first position of a compound. EXAMPLE: 花火 (はなび: fireworks) combines はな (the kun-yomi of 花) with ひ (the kun-yomi of 火). When these two kanji unite, ひ changes to び, because that makes it easier to pronounce. These sorts of changes match those that occur when adding a tenten, ゛, to certain kana. For instance, k becomes g; s becomes z; sh becomes j; and h becomes b. H can also become p, which is the equivalent of taking a yomi starting with h and adding a maru, ゜. EXAMPLE: 出発 (しゅっぱつ: departure) combines シュツ and ハツ, and when these two yomi unite, the ハ becomes パ. Teachers and textbooks routinely refer to these phonetic alterations as "voicing," and Joy o' Kanji uses the same term. However, phonetics experts say that this nomenclature is inaccurate. "Voicing" is a linguistics term for certain sounds that activate our vocal cords. In Japanese, the correct term for altered sounds such as the び of 花火 is 濁音 (だくおん). As 濁 means "muddy," 濁音 literally means that sounds have been "muddied"! The ぱ in しゅっぱつ is called 半濁音 (はんだくおん), reflecting that p sounds are only halfway (半) muddy! By contrast, sounds such as ひ and は are "clear"; that is, they're 清音 (せいおん). The process of muddying sounds is known as 濁り (にごり). More specifically, the muddying that occurs when two yomi meet in a compound is 連濁 (れんだく). Here at Joy o' Kanji, we're going to act as if we never heard these more precise definitions. (What's the word for the sound made when you insert your fingers in your ears to tune out unwelcome noise?) For our purposes, "voicing" will be an all-purpose term referring to any phonetic changes made to a yomi when parts of a compound come together. Deal?

Putting It All Together: The following compound unites 金 (gold) and 山 (mountain, mine):

金山(きんざん: gold mine)        

Here, the on-yomi キン has united with the on-yomi サン. Voicing has changed サン to ザン. Note that the yomi of a whole word conventionally appears in hiragana, regardless of whether that yomi represents multiple kun-yomi or several on-yomi. So it is that we represent the yomi of 金山 as きんざん, rather than キンザン.


How Kanji Combine in Compounds

Kanji often combine in unpredictable ways. The rules tend to be most regular in compounds featuring only on-yomi. 

on-on combination: Compound that you read by using the on-yomi of each kanji. EXAMPLE: With 住所 (address), use the on-yomi of 住 (ジュウ) and the on-yomi of 所 (ショ) to get じゅうしょ. 

kun-kun combination: Compound that you read by using the kun-yomi of each kanji. EXAMPLE: With 名前 (name), use the kun-yomi of 名 (な) and the kun-yomi of 前 (まえ) to produce なまえ. 

You may know 一番 as いちばん (best; first; number one). That's an on-on combination. But you can also read this word as a kun-kun combination, and when you do, the meanings change! The yomi becomes ひとつがい, and the word then means "pair." Specifically, ひとつがい tends to refer to a couple of animals of the same species, one male and one female. To indicate this meaning, people usually write ひとつがい in hiragana, as the kanji would lead readers astray. How wonderfully dynamic compounds are!

okurigana (送り仮名): Hiragana that trail after kanji or that pop up between kanji, as in 送り仮名, which is the very word okurigana. The first "Putting It All Together" (The Japanese Scripts) featured okurigana—namely, the ます of 書きます. Then, in the definition of "singleton" (Singletons and Compounds), you saw 行く (to go) represented as い•く. In verbs or adjectives, anything after the raised dot is okurigana. People often use parentheses to set off okurigana, but Joy o' Kanji uses a raised dot to avoid an excess of parentheses. Okurigana are necessary because the Japanese can write most nouns entirely with kanji but need hiragana to indicate the inflections of verbs and adjectives, among other things. Singletons generally have okurigana. EXAMPLE: 明るい, 明かり, and 明ける. This helps you know to use their kun-yomi: あかるい (bright), あかり (light, clearness), and あける (to become light). By contrast, most compounds don't have okurigana. EXAMPLE: the on-on combination 明白 (めいはく: clear, unmistakable). However, kun-kun combinations sometimes have final okurigana, as in 夜明け (よあけ: dawn), or interstitial okurigana, as in 送り仮名 (おくりがな). There may be two acceptable ways of writing a Japanese term. EXAMPLE: 気持ち and 気持 both represent きもち (feelings). Whereas 気持ち is the official reading, 気持 is informal. Dictionaries sometimes conflict about these sorts of okurigana variations. In such cases, I defer to the authority of Kojien, the most prestigious dictionary in Japan.

jubako-yomi (重箱読み, じゅうばこよみ): Words connecting an initial on-yomi with a kun-yomi. EXAMPLE: 本屋 (ほんや: bookshop) combines the on-yomi ホン with the kun-yomi や. For another example, consider 重箱 (じゅうばこ)! This word (which means "multi-tiered food box; stacked boxes") unites the on-yomi ジュウ with the kun-yomi はこ.

yuto-yomi (湯桶読み, ゆとうよみ): Words connecting an initial kun-yomi with an on-yomi. EXAMPLE: 場所 (ばしょ: place) combines the kun-yomi ば with the on-yomi ショ. And 湯桶 itself (meaning "pail-like wooden container typically lacquered in Japanese style, used for holding and serving hot liquids") joins the kun-yomi ゆ with the on-yomi トウ. The second kanji, 桶, is non-Joyo.

A sign for a pickle shop offers a treat that has nothing to do with food. Though there are just a dozen kanji here, we find a delicious collection of yomi combinations. Inside the radish picture in the middle (which we need to read from right to left because this is an old sign), we find this:

千枚漬 (せんまいづけ: pickled sliced radishes)     on + on + kun

As the red text indicates, we have two on-yomi and then a kun-yomi.

Down the right side we have this word:

銀閣寺道 (ぎんかくじみち: Ginkakuji Temple Road)     on + on + on + kun

All are on-yomi except for 道 as みち, which is a kun-yomi.

On the left, these are the three smaller characters:

京漬物 (きょうつけもの: Kyoto pickle)     on + kun + kun

We could consider this a jubako-yomi! How thrilling! Actually, some might say that this word doesn't qualify as such. That's because the "real" compound here is 漬物, (pickle); the 京- prefix appears just in this situation. Moreover, many sources say that only a two-character compound can have a jubako-yomi or yuto-yomi. However, other sources define these terms more broadly, extending them even to three-character compounds. At any rate, let's throw caution to the wind and celebrate the rare sighting.

Finally, what is likely the owner's surname is a kun-kun combination:

小松 (こまつ: surname)      kun + kun

In Japan, it's quite common to read both family names and given names as kun-kun combinations.

Further Reading: For more on the following topics, see these parts of Crazy for Kanji

kun-kun combinations: Exhibit 39
okurigana: Exhibit 18
jubako-yomi and yuto-yomi: Exhibit 39



ateji (当て字): Kanji whose usual sounds or meanings do not apply in the context of a particular word. There are several types of ateji. In one type, the Japanese selected kanji for their meanings, with no regard for their sounds. EXAMPLE: 無花果 (いちじく: fig). None of these kanji carries the sounds い, ち, じ, or く. But the meaning (not + flower + fruit) matches the old Japanese perception of the fig, which had visible fruit but flowers that were not visible. In another type of ateji, the Japanese chose kanji based on their sounds, with no regard for their meanings. EXAMPLE: 寿司 (すし). The characters have the sounds ス and シ, respectively, and mean "longevity" and "to govern."

jukujikun (熟字訓): An irregular set yomi for a particular compound. The reading of the whole word is official and established (i.e., Joyo), even though it's often impossible to determine which part of that whole yomi corresponds to which kanji. EXAMPLES: 今日 (きょう: today), 明日 (あした or あす: tomorrow), 昨日 (きのう: yesterday), and 上手 (じょうず: skillful). It's intuitive to divide 上手 as じょう + ず, but 手 has no such yomi as ず (or す). Still, じょうず is considered a Joyo yomi as a whole. Some notes on jukujikun: 

• Sometimes, though, one can say for sure which kanji goes with which part of the whole yomi of a jukujikun. That's true, for instance, when a compound yokes a Joyo yomi with a non-Joyo yomi. EXAMPLE芝生 (しばふ: lawn) breaks down as しば (a Joyo yomi of ) + ふ (a non-Joyo reading of 生). EXAMPLE大阪 (おおさか: Osaka) breaks down as おお (a Joyo yomi for 大) + さか (a non-Joyo reading of 阪).

• There are also situations in which a compound contains only non-Joyo yomi. EXAMPLE凹凸 (おうとつ: unevenness; roughness; ruggedness) follows the Joyo rules (with 凹 as おう and 凸 as とつ), but the inverted compound 凸凹 (でこぼこ: (1) unevenness; roughness; ruggedness; (2) inequality) does not. We know that 凸 corresponds to でこ and that 凹 goes with ぼこ, but those characters don't officially carry those sounds. Still でこぼこ is recognized as the Joyo yomi of 凸凹 as a whole.

• In 熟字訓, the 訓 (kun) suggests that we're talking about kun-yomi. The readings above certainly aren't on-yomi, as they couldn't have come from Chinese. But it's questionable as to whether a jukujikun is technically a kun-yomi.

• A jukujikun is the second type of ateji mentioned above; that is, it consists of kanji chosen for their meanings with no regard for their sounds. 

Further Reading: For much more on the following topics, see these parts of Crazy for Kanji:

ateji: Exhibit 36 
jukujikun: Exhibit 36 (the section called Type 2)

Components, Radicals, Phonetics, and the On-Echo

Far from being random collections of strokes, kanji have distinct parts that serve purposes, much as walls, ceilings, and floors contribute to a building's functionality. The distinct parts of a kanji are known as "components." There are three types: the radical, the phonetic, and components.

component (構成部分, こうせいぶぶん: lit. "composition part," or 構成要素, こうせいようそ, lit. "composition element"): Indivisible unit of meaning inside a character. Some characters consist of just one component. EXAMPLE: 大 (big) contains just one component: 大. Other kanji have several components. EXAMPLE: 照 (to illuminate) contains four components: 日 (sun, day), 刀 (sword), 口 (opening), and 灬 (fire). 

radical (部首, ぶしゅ): The component that enables people to categorize kanji and therefore to locate them in dictionaries. The radical may have a clear meaning. EXAMPLES: 艹 (grass), 宀 (roof), and刂 (sword). That meaning may relate to the meaning of the whole kanji. EXAMPLE: 艹 is the radical in 薬 (medicine). This makes sense; medicines often come from grasses or plants. In other characters, the meaning of the radical is irrelevant to the significance of the whole kanji. EXAMPLE: The 宀 (roof) in 字 (character, letter) no longer has anything to do with the meaning of 字, though there was once a connection; 字 originally meant bringing up a lot of children in a house (i.e., under a roof) and has come to mean "characters" because characters multiply just like children.

phonetic component (音符, おんぷ): The part of a character that tells us how that character sounds. Not all kanji contain phonetic components (also called simply "the phonetic"), but at least two-thirds do. When you can split a kanji into left-hand and right-hand sides, the radical will typically be on the left, the phonetic on the right. The on-yomi of the phonetic may match the on-yomi of the whole character. EXAMPLE: The left side of 時 is the radical 日. The phonetic 寺 is the remainder. The phonetic 寺 has the on-yomi of ジ, as does 時. 

on-echo (a term that Eve coined): Instances in which two or more kanji have a common phonetic component and the same on-yomi. EXAMPLE: 安, 案, 按, and 鮟 share the phonetic 安 and the on-yomi アン. This shared shape may have no bearing on meaning. About 20 percent of Joyo kanji belong to a series of characters with on-echoes. When the main character in any Joy o' Kanji essay is part of an echoing series, you'll see members of that series marked in blue in the look-alikes section of the Character Profile. Some notes on how on-echoes work: 

• The echoing shape may not have the same yomi as the kanji sharing the shape. For instance, 地, 池, and the non-Joyo 馳 have the yomi of チ. Not so for the non-Joyo 也, the shape they all share. It's read as ヤ.

• The echoing shape may not be a complete kanji (as with 㑒, which heads a ケン series that includes 験 and 剣).

• The series needn't be large to qualify as a series.

• Some of the echoes in a series may be voiced; the family may consist of both ホウ and ボウ sounds or of both カクand ガク yomi. If you spot characters whose shapes and yomi are similar, it's tempting to wonder whether they form a family. That could happen with 肩 (ケン), 偏 (ヘン), and 扇 (セン). But these do not conform to voicing patterns; that is, k (from ケン), h (from ヘン), and s (from セン) have nothing to do with each other. Therefore, these characters are not part of the same on-echo series.

To determine whether characters belong to a series, I rely on an excellent and out-of-print book—Michael Pye's The Study of Kanji (Hokuseido Press: 1971).

Putting It All Together: It can be tricky to identify the radical, the phonetic, and components. For instance, you may be tempted to see 架 (カ, か•ける: to lay across) as consisting of three components, any of which could be the radical. But in 架, the radical is 木, whereas 加 is the phonetic. As it turns out, 加 (addition, increase) is a kanji in its own right and has the on-yomi of カ. The phonetic 加 lends its on-yomi to 架. The kanji 賀 (congratulations) is also part of this on-echo series, but its yomi has mutated from カ to ガ.

Further Reading: For much more on radicals, including an explanation of "on-duty radical" and "off-duty radical" (two more terms that Eve coined), see Radical Terms and Radical Notes. And for more on the following topics, see these parts of Crazy for Kanji:

the "architecture" of kanji: pages 51–52
radicals versus components: Exhibit 24 
on-echo: Exhibit 26

Old-Style Scripts, Yojijukugo, and Kokuji

old-style scripts: In the Etymology Box of each essay, the ancient versions of characters come from Richard Sears's site, Chinese Etymology. He has kindly given me permission to reuse the images. Sears has categorized characters in several ways. Here's what his terms mean:

oracle characters: 1766 BCE – 1122 BCE
In this ancient era, a Chinese person with a pressing question would go to a fortune teller, who would take a turtle shell or ox scapula (shoulder blade) and inscribe the question. After that, the fortune teller would expose the shell or scapula to fire. By observing how it cracked, the fortune teller would predict the future. The characters still legible from that period obviously escaped burning.

bronze characters: 1122 BCE – 221 BCE
Many of the characters surviving from this era have been found on objects cast in bronze. The inscriptions typically commemorated important events, rather than describing everyday concerns.

seal characters: 221 BCE – 200 CE
The Chinese used—and continue to use—this style of character for some official documents and for official seals. The Japanese also use this script for official seals.

Photo Credit: Lutlam

A wrapper for chopsticks features the words 禅味 and 寿 in seal script. The 寿 (ことぶき: longevity; congratulations; celebration) is the name of the restaurant. Meanwhile, 禅味 (ぜんみ) can mean "the flavor of Zen." It's often used in the names of restaurants serving healthy Japanese food, such as soba or vegetarian fare.

Sometimes Sears refers to LST seal characters. This stands for "LiuShuTong," a collection of all the characters, both standard and nonstandard, that were known to exist anywhere up until the Ming dynasty (1368 CE – 1644 CE). There are more than 38,000 LST characters.

These categories constitute historical periods, but these were not the eras in which the characters originated. Understanding the categories requires some context.

Probably as early as 2300 BCE (and definitely by 1500 BCE), says Sears, the Chinese created books by using reed pens to draw characters on bamboo slats. However, that came to a halt when Qin Shi Huang became emperor of China in 221 BCE and decreed that most books (that is, bamboo slats) be burned. Not a single bamboo slat has survived to modern times. To know how ancient characters looked, scholars such as Sears have had to content themselves mainly with oracle bones and bronzes.

For a single character such as 馬 (horse), Sears provides dozens of images from all three periods, as well as a wide array of LST seal characters. The oracle horses look like hieroglyphics from caves. The bronze horses have fishy shapes. The seal-script character looks extra-hairy. Finally, some of the many LST seal characters resemble the 馬 kanji we know today.

One might think that the variations among the horse images would show how the character evolved over time, and that could be true. But Sears notes something much more crucial and fascinating: "These characters may have differed from the actual characters used at the time. It is very difficult to cast a bronze character that looks as good as one written by brush. Also, it is almost impossible to inscribe a curved line on a turtle bone, so when we look at the oracle bone characters, we may get a distorted picture of the usual characters of the time."

Photo Credit: Lutlam

Stone lantern in a graveyard. The writing probably says 獻燈
(けんとう: votive lantern), most likely in bronze script. Both characters are non-Joyo. In modern writing, this word would be

yojijukugo (四字熟語): four-character compounds, most of which come from old Chinese poems that told stories in four lines or four stanzas. The first line served as an introduction, the second developed the premise, the third produced a climax or an unexpected change, and the fourth brought the story to a conclusion. The four characters in yojijukugo now represent those tales in a pithy way. These compounds are considered idiomatic because the whole says something different from the sum of its parts. Therefore, a breakdown of the compound may not capture the meaning of any given saying.

kokuji (国字): kanji invented in Japan from preexisting components. That is, the components came from China, but the arrangement and composite meaning are strictly Japanese. An example is 畑 (はたけ: field of crops). Kokuji in the Joyo set don't have on-yomi, with the exceptions of 働 (ドウ, はたら•く: to work), 搾 (サク, しぼる: to squeeze), and 塀 (ヘイ: fence; boundary wall; wall).

Further Reading: For more on the following topics, see these parts of Crazy for Kanji

typefaces: Exhibit 57 
yojijukugo: Exhibit 55
kokuji: Exhibit 30

Note on Italicization

In English-language writing, it's customary to italicize words borrowed from foreign languages. Therefore, one would expect to see terms such as kanji and yomi in italics. However, that leads to a preponderance of italics, which become annoying to read and perhaps even more annoying to code en masse. Therefore, in Joy o' Kanji you won't see italics used for the tools of the trade, the words with which people discuss the workings of kanji. Instead, italics will appear mainly for Japanese words used as words (e.g., "That's the kanji for the word hiragana"). Italics will also differentiate words that look alike in both English and romanized Japanese; for that reason, "on readings" includes italics, and "kun readings" does, too, for parallelism. You may see italics a few more times, but those other uses would be tedious to list here. No annoyance or tedium allowed in Joy o' Kanji! That would lead to a reduction of joy!