Cadenza

In music, a cadenza (from Italian: cadenza [kaˈdɛntsa], meaning cadence; plural, cadenze [kaˈdɛntse]) is, generically, an improvised or written-out ornamental passage played or sung by a soloist or soloists, usually in a "free" rhythmic style, and often allowing for virtuosic display. During this time the accompaniment will rest, or sustain a note or chord. Thus an improvised cadenza is indicated in written notation by a fermata in all parts. A cadenza usually will occur over the final or penultimate note in a piece, or over the final or penultimate note in an important subsection of a piece. It can also be found before a final coda or ritornello.

The term cadenza often refers to a portion of a concerto in which the orchestra stops playing, leaving the soloist to play alone in free time (without a strict, regular pulse) and can be written or improvised, depending on what the composer specifies. Sometimes, the cadenza will include small parts for other instruments besides the soloist; an example is in Sergei Rachmaninoff's Piano Concerto No. 3, where a solo flute, clarinet and horn are used over rippling arpeggios in the piano. The cadenza normally occurs near the end of the first movement, though it can be at any point in a concerto. An example is Tchaikovsky's First Piano Concerto, where in the first five minutes a cadenza is used. The cadenza is usually the most elaborate and virtuosic part that the solo instrument plays during the whole piece. At the end of the cadenza, the orchestra re-enters, and generally finishes off the movement on their own, or, less often, with the solo instrument.

...
Wikipedia