What does the term "a cappella" mean?

The term "a cappella" refers specifically to choral music that is performed without any instrumental accompaniment. This means that all vocal parts—soprano, alto, tenor, and bass—are sung solely by the voices of the singers, creating harmonies and melodies purely through vocalization. The absence of instruments allows for a focus on the vocalists' harmonies and techniques, often highlighting the complexities of vocal arrangements.

The other options do not accurately convey the definition of "a cappella." For instance, vocal music accompanied by piano includes instrumentation, directly contradicting the essence of a cappella. Similarly, music written solely for string instruments and choral music that includes a rehearsal piano both imply the presence of specific instruments, which is not aligned with the concept of a cappella singing. Each of these alternatives introduces an element of accompaniment that is not present in a true a cappella performance.