What term describes the Baroque genre that contrasts a small ensemble of solo instruments with a larger ensemble?

The term that describes the Baroque genre contrasting a small ensemble of solo instruments with a larger ensemble is indeed the concerto grosso. This form features a "concertino," which is the group of solo instruments, and a "ripieno," which refers to the larger orchestra. The interplay between the two groups creates a rich tapestry of sound, highlighting the virtuosity of the soloists while also benefiting from the fuller textures provided by the larger ensemble.

In concerto grosso compositions, the conversations and contrasts between the soloists and the orchestra are central to the musical experience, making this genre distinctive during the Baroque period. The structure typically involves various movements, often with contrasting tempos and styles. Other terms, like sonata form, fugue, and suite, define different musical concepts and structures, not centered on this specific contrast between small and large ensembles.