In music, form describes the overall structure or plan of a song or piece of music, and it describes the layout of a composition as divided into sections. In the early 20th century, Tin Pan Alley songs and Broadway musical songs were often in AABA 32 bar form, in which the A sections repeated the same eight bar melody (with variation) and the B section provided a contrasting melody or harmony for eight bars. From the 1960s onward, Western pop and rock songs are often in verse-chorus form, which is based around a sequence of verse and chorus ("refrain") sections, with new lyrics for most verses and repeating lyrics for the choruses. Popular music often makes use of strophic form, sometimes in conjunction with the twelve bar blues.