Addendum

An addendum is an add-on to a contract. It attaches new terms, schedules, or details to an agreement without disturbing the original language. A master agreement plus an addendum that lists specific deliverables is a common pattern.

The line between an addendum and an amendment is worth knowing: an addendum adds, an amendment changes. In practice the terms are sometimes used loosely, so what matters is that the document clearly states whether it is adding to or modifying the original, and that both parties sign it.