According to the Records of Rites and Music in the Book of Han, during the reign of Emperor Wu of the Han Dynasty, there was an organization called "Yuefu" that collected songs from various places and organized and formulated music scores. Later, people called the poems collected and composed by this institution Yuefu poems, or simply Yuefu. By the Tang Dynasty, although the music scores of these poems had long been lost, this form was passed down and became a poetry genre without strict meter and close to five or seven character ancient poems. In essence, songwriting is similar to today's pop songs. There are no strict rhythm requirements. As long as they sound good and can clearly express one's emotions.