Yuefu (乐府) poems were written in the Han Dynasty. Originally, yuefu was a government office set up by the imperial court to train musicians, collect folk songs and ballads, compose music, and match musical instruments to it. It later came to refer to folk songs and ballads collected, matched with music, and played by court musicians. Poems of this style represented a new creation of ancient folk songs and ballads in the years after The Book of Songs was compiled, and equaled The Book of Songs and Odes of Chu in importance. About 50 to 60 yuefu poems have been handed down to this day. They truthfully depicted various aspects of society at the time and revealed genuine emotions, thus creating a literary tradition reflecting ordinary people’s sentiments. In particular, yuefu poems were noted for their vivid depiction of women’s life. All poems that could be chanted or were written with yuefu themes were collectively called yuefu poems in later times.
After Emperor Wu of the Han Dynasty set up an office to collect folk songs and ballads, folk songs from the Dai and Zhao regions, and ballads from the Qin and Chu regions could be heard. They were all created to express people’s joy and sorrow or were inspired by certain events… (The History of the Han Dynasty)
Yuefu poems vary in rhythm and tone and are accompanied by music when chanted. (Liu Xie: The Literary Mind and the Carving of Dragons)