In rock music styles, notably heavy metal music, there is usually one or more guitar solos in the song, often found after the middle chorus part. The most common format in modern popular music is introduction (intro), verse, pre-chorus, chorus (or refrain), verse, pre-chorus, chorus, bridge ('middle eight'), verse, chorus and outro. Pop and traditional forms can be used even with songs that have structural differences in melodies. Popular music songs traditionally use the same music for each verse or stanza of lyrics (as opposed to songs that are 'through-composed'-an approach used in classical music art songs). Common forms include bar form, 32-bar form, verse–chorus form, ternary form, strophic form, and the 12-bar blues. It is typically sectional, which uses repeating forms in songs. Song structure is the arrangement of a song, and is a part of the songwriting process.
