What is the term used for a style of composition characterized by three or more voices entering in imitation of one another?

The term that describes a style of composition where three or more voices enter in imitation of one another is known as a fugue. In a fugue, a main theme or subject is introduced by one voice and subsequently echoed or imitated by other voices in a structured manner. This technique highlights the interdependence of the voices while maintaining the integrity of the original musical idea.

Fugues often feature specific formal elements, including exposition, development, and recapitulation, which showcase the voices' interactions and transformations as the composition progresses. The complex interplay of the imitative lines creates a rich tapestry of sound that is characteristic of this form, particularly in the works of composers such as Johann Sebastian Bach.

The other terms listed refer to different formal structures or concepts in music. For instance, a sonata is typically a multi-movement work for a solo instrument or chamber ensemble, while a sonatina is a shorter, simpler version of a sonata, often intended for teaching purposes. A theme, on the other hand, refers to a recognizable musical idea that can be developed or varied, but does not specifically denote the imitative approach found in a fugue.