What is Arrangement?

Legal Definition
In music, an arrangement is a musical reconceptualization of a previously composed work. It may differ from the original work by means of reharmonization, melodic paraphrasing, orchestration, or development of the formal structure. Arranging differs from orchestration in that the latter process is limited to the assignment of notes to instruments for performance by an orchestra, concert band, or other musical ensemble. Arranging "involves adding compositional techniques, such as new thematic material for introductions, transitions, or modulations, and endings.... Arranging is the art of giving an existing melody musical variety".
-- Wikipedia
Legal Definition
When a debtor and creditor make an agreement about repayment or a debt.