On'yomi refers to the Chinese readings of kanji, the characters used in the Japanese writing system. These readings were adopted from Chinese during various historical periods, leading to different pronunciations based on the time and region of origin. On'yomi is often used in compound words, where two or more kanji are combined to create new meanings. In contrast to on'yomi, there is another reading called kun'yomi, which is the native Japanese pronunciation of kanji. Understanding both on'yomi and kun'yomi is essential for mastering the use of kanji in the Japanese language, as they provide different ways to read and interpret the characters.