What defines an aria in the context of music?

An aria is defined as a self-contained solo vocal piece that typically expresses deep emotions and is often found in operas. This musical form allows the singer to showcase their vocal skill and emotion through elaborate melodies and rich harmonies. Arias usually serve as moments for character reflection or expression of feelings within the context of the larger narrative of the opera. They may also vary in structure, often incorporating verse and refrain, which further highlights the emotional content and complexity of the music.

The other options do not accurately capture the essence of an aria. For instance, a type of instrumental piece used in symphonies refers to entirely different musical forms that do not focus on vocal performance. A repeated motif, while significant in many musical contexts, does not pertain specifically to solo vocal works. Lastly, a vocal piece that includes multiple singers is more characteristic of a duet, chorus, or ensemble rather than the singular focus associated with an aria. Thus, the defining feature of an aria remains its solo vocal nature that emphasizes personal emotion and artistic expression, making the first choice the correct definition.