Types of Kanji
Types of Kanji: by Category
A Chinese scholar Xu Shen (許慎), in the Shuōwén Jiězì (說文解字) ca. 100 CE, classified Chinese characters into six categories (Japanese: 六書 rikusho). The traditional classification is still taught but is problematic and no longer the focus of modern lexicographic practice, as some categories are not clearly defined, nor are they mutually exclusive: the first four refer to structural composition, while the last two refer to usage.
(For a table of all the kyōiku kanji (教育漢字) broken down by category see this page, from which the above description has been extracted.)
Shōkei-moji (象形文字)
These characters are sketches of the object they represent. For example, 目 is an eye, 木 is a tree, etc. The current forms of the characters are very different from the original, and it is now hard to see the origin in many of these characters. It is somewhat easier to see in seal script. This kind of character is often called a "pictograph" in English (Shōkei -- 象形 is also the Japanese word for Egyptian hieroglyphs). These make up a small fraction of modern characters.
Shiji-moji (指示文字)
Shiji-moji are called "logograms", "simple ideographs", "simple indicatives", and sometimes just "symbols" in English. They are usually graphically simple and represent an abstract concept such as a direction: e.g. 上 representing "up" or "above" and 下 representing "down" or "below". These make up a tiny fraction of modern characters.
Kaii-moji (会意文字)
Often called "compound indicatives", "associative compounds", "compound ideographs", or just "ideographs". These are usually a combination of pictographs that combine to present an overall meaning. An example is the kokuji 峠 (mountain pass) made from 山 (mountain), 上 (up) and 下 (down). Another is 休 (rest) from 人 (person) and 木 (tree). These make up a tiny fraction of modern characters.
Keisei-moji (形声文字)
These are called "phono-semantic", "semantic-phonetic", "semasio-phonetic" or "phonetic-ideographic" characters in English. They are by far the largest category, making up about 90% of characters. Typically they are made up of two components, one of which indicates the meaning or semantic context, and the other the pronunciation. (The pronunciation really relates to the original Chinese, and may now only be distantly detectable in the modern Japanese on'yomi of the kanji. The same is true of the semantic context, which may have changed over the centuries or in the transition from Chinese to Japanese. As a result, it is a common error in folk etymology to fail to recognize a phono-semantic compound, typically instead inventing a compound-indicative explanation.)
As examples of this, consider the kanji with the 言 shape: 語, 記, 訳, 説, etc. All are related to word/language/meaning. Similarly kanji with the 雨 (rain) shape (雲, 電, 雷, 雪, 霜, etc.) are almost invariably related to weather. Kanji with the 寺 (temple) shape on the right (詩, 持, 時, 侍, etc.) usually have an on'yomi of "shi" or "ji". Sometimes one can guess the meaning and/or reading simply from the components. However, exceptions do exist -- for example, neither 需 nor 霊 have anything to do with weather (at least in their modern usage), and 待 has an on'yomi of "tai". That is, a component may play a semantic role in one compound, but a phonetic role in another.
Tenchū-moji (転注文字)
This group have variously been called "derivative characters", or "mutually explanatory" or "mutually synonymous" characters; this is the most problematic of the six categories, as it is vaguely defined. It may refer to kanji where the meaning or application has become extended. For example, 楽 is used for 'music' and 'comfort, ease', with different pronunciations in Chinese reflected in the two different on'yomi, gaku 'music' and raku 'pleasure'.
Kashaku-moji (仮借文字)
These are called "phonetic loan characters." For example, 来 in ancient Chinese was originally a pictograph for 'wheat'. Its syllable was homophonous with the verb meaning 'to come' and the character is used for that verb as a result, without any embellishing "meaning" element attached.
Source: Wikipedia