Kanji
Kanji (漢 字, "Chinese characters") is one of the three writing systems used in the Japanese language (the other two being the kana: hiragana and katakana). Unlike the kana, which represent syllables, kanji are pictograms representing concepts. They were imported over a period of centuries from the Chinese language, are typically more complex than kana, and have different meanings and pronounciations depending on how they are combined with other kanji and kana. A kanji will often have its current pronunciation spelled out in ruby characters known as "furigana," small hiragana written above it or to its right.
Kanji have two categories of meanings and pronunciations, referred to as "readings:" on readings and kun readings. On readings are based loosely on the original Chinese uses of the character, and are typically used when a kanji is part of a compound. Kun readings are typically used when kanji are used on their own, either as complete nouns or as adjective and verb stems. Most kanji have at least one on-reading and one kun-reading each.
There are exceptions to these rules. Many kanji have no kun-reading and a few have no on-reading. Some use kun-readings, not on-readings, to make compounds.
Often a kanji will be used for the root of a verb, with the conjugation written in hiragana.