Wikipedia defines musical arrangement of a musical composition as a reworking of a piece of music so that it can be played by a different instrument or combination of instruments from the original. For example, a song written for one voice with piano accompaniment might be arranged so that it can be sung in parts by a choir, or a piece for violin might be arranged so that it can be played on a clarinet instead.
I do musical arrangements for school choirs or ensembles as well as for vocal jazz ensembles (A Cappella or otherwise). These arrangements can include rehearsal tracks, print-ready scores, etc.
Contact me for customized musical arrangements for your choir or ensemble, etc.