arrangement
An adaptation of a musical composition for different instruments or voices than originally intended.
In Depth
An arrangement takes an existing piece and reworks it for a different performing force. A symphony might be arranged for piano, a pop song for string quartet, or a jazz standard for big band. The arranger must capture the essence of the original while exploiting the capabilities of the new instruments.
Arranging is a distinct skill from composing — it requires deep knowledge of instrumentation, orchestration, and the original work's structure. Some arrangements become more famous than the originals: Ravel's orchestration of Mussorgsky's Pictures at an Exhibition and many jazz big band arrangements are definitive versions. In popular music, the arrangement — the choice of instruments, the backing vocal parts, the instrumental breaks — can make or break a song.
Ravel's orchestration of Mussorgsky's Pictures at an Exhibition is so famous that most people have never heard the original piano version — the arrangement eclipsed the original.