A concerto is a piece of music made for a solo instrument and an orchestra. When an orchestra plays at a concert they might play a symphony (a piece for orchestra) and they might play a concerto (with a soloist). If the solo instrument is a violin the piece is called a “violin concerto”, if it is a piano it is called a “piano concerto”, etc. The orchestra accompanies the soloist. This means that it is the soloist who decides how fast or slow to play. The conductor should listen to the way the soloist wants to play and make the orchestra accompany sensitively.