cadenza
A virtuosic solo passage near the end of a concerto movement, often improvised or written out.
In Depth
A cadenza is a moment in a concerto where the orchestra stops and the soloist plays alone, often with great virtuosity and freedom. In the Classical era, cadenzas were improvised by the performer. By the Romantic period, composers began writing them out, though some performers still compose their own.
The cadenza typically occurs near the end of a movement, signalled by the orchestra landing on a sustained chord. The soloist then elaborates on the movement's themes, demonstrating technical brilliance before a trill signals the orchestra to re-enter. Beethoven's written-out cadenzas for his piano concertos set the standard for the composed cadenza.
Mozart's father once wrote to him complaining that his concerto cadenzas were too long — the audience wanted to applaud but couldn't find the right moment.