Wikipedia
Yayue was originally a form of Chinese classical music that was performed at imperial courts. The basic conventions of yayue were established in the Western Zhou. Together with law and rites, it formed the formal representation of aristocratic political power.
The word ya (雅) was used during the Zhou Dynasty to refer to a form of song-texts used in court collected in Shijing. The term yayue itself first appeared in the Analects, where yayue was considered by Confucius to be the kind of music that is good and beneficial, in contrast to the popular music originated from the state of Zheng which he judged to be decadent and corrupting. Yayue is therefore regarded in the Confucian system as the proper form of music that is refined, improving, and essential for self-cultivation, and one that can symbolize good and stable governance. It means the kind of solemn ceremonial music used in court, as well as ritual music used in temples including those used for Confucian rites. In a broader sense, yayue can mean a form of music that is distinguishable from the popular form of music termed suyue (俗樂) or "uncultivated music", and can therefore also include music of the literati such as qin music.
The court yayue has largely disappeared from China, although there are modern attempts at its reconstruction. In Taiwan yayue is performed as part of a Confucian ceremony, and in China in a revived form as entertainment for tourists. Other forms of yayue are still found in parts of East Asia, notably the gagaku in Japan, aak in Korea, and nhã nhạc in Vietnam. Although the same word is used (but pronounced differently), the music does not necessarily correspond to Chinese yayue. The Korean aak however preserved elements of Song dynasty yayue long lost in China.