Kanji usually have a kun-yomi (訓読み) and an on-yomi (音読み) reading, although they may have only one of these, or have several of each. The character 生, for example, can be read in at least 16 ways.
Kun-yomi readings are used where a kanji represents a native Japanese word. On-yomi readings are approximations of Chinese pronunciation, and usually occur in compound words. Where furigana (ruby) is used, kun-yomi readings can be written in either hiragana or katakana, while on-yomi readings are almost always written in hiragana.
車 | くるま | kuruma | car |
電車 | でんしゃ | densha | train |
In the above example, kuruma is the kun-yomi reading, and sha is the on-yomi reading.
In iKanji and most dictionaries, kun-yomi are always written in hiragana, and on-yomi are always written in katakana. This is so there is a clear differentiation between the two.