Unlike the concerto, where the soloist is accompanied by an orchestra, a uses a piano to accompany the soloist.

Grosso cannot be the answer since Grosso is a form of concerto still that transitions to a full orchestra. Madrigal as well is a  group of singers singing songs in the Rennaissance age. Cantata is accompanied by a choir which means the answer is Sonata which is accompanied usually by a pianist.

The term is called adduction 

If you could give us the questions i can see if i can you! : )