song form
A ternary structure (ABA) widely used in art song, popular song, and instrumental music
In Depth
Song form, also called ternary form or ABA form, presents a theme (A), a contrasting middle section (B), and a return of the opening theme (A). In popular music, the 32-bar AABA form became the dominant structure for Tin Pan Alley standards and jazz standards from the 1920s through the 1950s. The B section is called the bridge or middle eight. The form provides both contrast and unity, making it one of the most psychologically satisfying musical structures.
Over the Rainbow, Somewhere Over the Rainbow, and thousands of other Great American Songbook standards all follow the 32-bar AABA song form.