What term refers to a musical form consisting of two different sections labeled A and B?

The term that refers to a musical form consisting of two different sections labeled A and B is "Binary." In binary form, there are two distinct parts, usually represented as A and B, where each section typically contrasts in melody, harmony, or mood. The A section presents the initial musical idea, while the B section often offers a contrasting theme or variation before returning to the A section in certain contexts.

On the other hand, "Ternary" refers to a form that consists of three sections, commonly structured as A-B-A, where A is repeated after the contrasting B section. "Sonata" describes a more complex form typically used in classical compositions that often involves multiple themes and is structured in multiple sections, including exposition, development, and recapitulation. "Fugue" is a specialized type of contrapuntal composition that revolves around the interplay of multiple melodic lines (voices) and is characterized by the systematic presentation and development of a main theme, rather than the simple duality of a binary form.