What kind of poem is Pipa Xing?

Seven-character Songs Seven-character Songs originated from ancient Yuefu and Cao Pi's Ge Yanxing, which flourished in the Tang Dynasty. It is a special style, and words such as "Song" and "Xing" often appear in poetry titles. It is a poetic genre that can be sung with music. The number of general sentences is uncertain, and the number of words in each sentence is not fixed. Can be mixed with three or five sentences, but mainly seven words. The purpose of seven-character song creation is to imitate the lyrics, and its style is determined by the lyrics suitable for singing.