What is it called when the Constitution is formally changed?

The term used when the Constitution is formally changed is "amendment." This process involves officially altering the text of the Constitution to add, modify, or revoke provisions. An amendment can be proposed either by a two-thirds majority in both the House of Representatives and the Senate or by a convention called for by two-thirds of state legislatures. Once proposed, it must be ratified by three-fourths of the state legislatures or by conventions in three-fourths of the states to become law.

Other terms like "revision" suggest a broader or more sweeping change which is not how amendments function, as they focus on specific alterations rather than a complete overhaul of the document. "Ratification" refers specifically to the process of approving an amendment after it has been proposed, rather than the act of changing the Constitution itself. "Reformation" is a broader term related to change or improvement in a social or political context, but does not accurately describe the formal process for constitutional changes. Therefore, "amendment" is the precise term for this important constitutional procedure.