A word is a language unit composed of morphemes, which is one level higher than morphemes. A word is the smallest language unit that can be used independently. "Independent use" refers to being able to speak alone (to form a sentence alone) or to use alone (to be a syntactic component alone or to play a grammatical role alone). Word formation is: process keyword arrangement. At first, words were sung by music, so writing words was also called lyrics, relying on sound. Words were originally called "songs" or "songs". Qin's interest and poetry are accompanied by music. From the music point of view, it is the same literary genre as Yuefu, and it also comes from folk literature. Later, Ci, like Yuefu, gradually separated from music and became a different style of poetry, so some people called Ci "poetry". Scholars' Ci is deeply influenced by metrical poems, so there are many metrical sentences in Ci. Words can be roughly divided into three categories: (1) poems. (2) alto; (3) Long tune.