An act in the legal sense refers to either a voluntary bodily movement or a term for a body of law/proposed law.
In the criminal law context, an act is part of the concept of actus reus and, therefore, is a prerequisite to finding a defendant guilty. To qualify as an act, a movement must be voluntary. Although most crimes require that the prosecution proves an act occurred, a breach of a duty to act, known as an omission, can also satisfy the actus reus requirement.
Regarding legislation, an act is a term for a formal body of law. Frequently, a collection of provisions regarding the same subject are known as an act like the Clean Water Act or the Civil Rights Act. Proposed legislation is also sometimes known as an act.
[Last updated in June of 2022 by the Wex Definitions Team]