The Young Lions vocabulary

A composition (usually in symphonic form with three movements) in which one instrument (or two or three) stands out in bold relief against the orchestra, or accompaniment, so as to display its qualities or the performer's skill.

^{- From The Collaborative International Dictionary of English v.0.48}

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a musical composition generally composed of three movements, in which either one solo instrument (for instance, a piano, violin, cello or flute) or a group of soloists (concertino) is accompanied by an orchestra or concert band. Its characteristics and definition have changed over time. In the 17th century, sacred works for voices and orchestra were typically called concertos, as reflected by J. S. Bach's usage of the title "concerto" for many of the works that we know as cantatas. [...]