What describes a "cadenza" in a musical composition?

A cadenza is characterized by a soloist performing a passage without accompaniment, allowing for a display of virtuosity and personal expression. Typically found in concertos, this section enables the soloist to elaborate on the themes or melodies present in the piece, often showcasing technical skill and interpretive ability. The cadenza usually occurs at a dramatic point in the composition, often before a return to the orchestra, emphasizing the individuality of the solo performer in a way that complements the overall work.

The other options describe different musical elements that do not align with the definition of a cadenza. A formal introduction, for instance, sets up the piece but does not feature the soloist in such a prominent way. Similarly, a repeated refrain counts as a recurring motif or phrase within a song, while a concluding section of a symphony would be related to the overall structure and finality of the piece rather than showcasing a single performer’s abilities.