Kanji (Chinese characters) have two different readings – the onyomi and the kunyomi. The onyomi is closer to the original Chinese language and is mostly used for nouns. One Kanji can have more than one onyomi.
The kunyomi reading is used to show the traditional Japanese pronunciation. It is most frequently used when kanji appear in adjectives or verbs.
Kanji can have multiple onyomu or kunyomi readings, and sometimes they might only have onyomi or kunyomi readings.
The Japanese government selected 1945 kanji to be used for official publications. These so called “toyo kanji” which are also used for the Japanese Language Proficiency Test (JLPT) have around 4000 readings.