Kanji have two sorts of readings, i.e. ways of being pronounced: "on" readings and "kun" readings.

The "on" readings are based loosely on the original Chinese pronunciation of the kanji, and are typically used when a kanji is part of a compound, i.e. written with at least one other kanji to form a word.

The "kun" reading is used when kanji are used on their own, either as complete nouns in their own right or as adjective and verb stems.