What is a musical piece in which one solo instrument(such as piano or violin ) is ac accompained by orchestra?

Answer 1

A concerto is a work in three movements, rather than the four movements of a symphony, in which a solo instrument or ensemble is accompanied by an orchestra. The concerto developed earlier than the symphony. As in the symphony, the first movement of the classical concerto is generally in sonata-allegro form, followed by a slow movement and a finale usually in rondo form. The concerto had arisen in the Baroque period, in two types. One was the concerto grosso, in which a small ensemble within the orchestra is contrasted to and accompanied by the full complement. The other was the solo concerto as described.