What is the term for a modification of the U.S. Constitution or a U.S. law?

The term for a modification of the U.S. Constitution or a U.S. law is "Amendment." This term specifically refers to a formal change or addition made to the Constitution or statute, which alters its original language or provisions. In the context of the U.S. Constitution, amendments can be proposed by a two-thirds vote in both houses of Congress or by a convention called for by two-thirds of state legislatures. Once proposed, an amendment must be ratified by three-fourths of the state legislatures or by conventions in three-fourths of the states to become effective.

Other terms, while they may refer to changes or adjustments, do not have the same formal and legal significance as "amendment." "Change" is a broad term that does not specifically indicate a legal alteration; "reform" typically refers to broader improvements or restructurings and may not involve formal statutory changes; and "revision" often suggests a reworking or editing process but lacks the legal specificity that "amendment" carries in the context of constitutional law and statutes.