What is a "coda" in a musical composition?

A "coda" in a musical composition refers specifically to a concluding section that serves to reinforce the main themes of the piece. Its purpose is to wrap up the musical ideas presented earlier, often returning to earlier motifs or themes, and providing a sense of closure. The coda can create a memorable finality, bringing the work to a satisfying finish by revisiting established material in a new context or through varied treatment.

The coda is typically positioned at the end of a piece, distinct from other sections that may introduce new themes or ideas. In contrast, the other options describe different structural elements within music: introducing new themes would occur in an exposition or similar section, improvisation is more associated with genres that allow for free expression, and transitional phrases typically serve to connect different sections or movements rather than concluding the piece. Thus, recognizing the coda as a reinforcing, concluding element highlights its critical role in the overall structure and emotional impact of a composition.