A Sonata is a musical composition of several contrasting movements for one or two instruments. A symphony is a sonata for orchestra; a quartet is a sonata for four instruments and a concerto is a sonata for solo instrument and orchestra.
The term sonata form or sonata-allegro form refers to the design or plan frequently used in the first movement. It has three main parts: exposition, development, and recapitulation. Each of these main parts has sections arranged according to key relationships.