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 also kun'yomi, which represents the native Japanese readings of kanji. Understanding both readings is essential for mastering the Japanese language, as they are used in different contexts and can significantly affect the meaning of words.