What is a "coda" in a musical composition?

A "coda" is defined as a concluding section of a musical composition that serves to wrap up or finalize the piece. It typically appears at the end after the main themes have been presented and explored, providing closure to the musical narrative. The coda often revisits themes or motifs heard earlier in the piece but presents them in a transformed or summarized manner, which reinforces the overall structure and gives the listener a sense of completion.

In contrast, the other options describe different musical elements. A theme that introduces a piece refers to its exposition, while a repeated section in the middle of a piece describes a musical device known as a "refrain" or "verse." An independent musical interlude generally describes a section that may exist within a work but doesn't function specifically as a concluding segment. Thus, the definition of a coda aligns perfectly with the purpose of providing an ending, confirming that option B is the most accurate choice.