Ternary form is a musical form. It is also called song form or minuet and trio. These forms all have three distinct sections. The three sections are written in shorthand as ABA. The music in the A sections is the same, or very nearly the same. The music in the B section is different from the A sections. The B section usually provides some sort of musical contrast to the A sections. It may be composed in a different but related key, for example. The B section is often called the "trio", especially in minuets, scherzi, marches, polonaises, etc. The B section came to be called the "trio" because a Baroque composer consistently scored this section in his minuets for three instruments.