A more thorough explanation:

A legal excuse is a reason that justifies an act or omission or that relieves a person of a duty. In criminal law, it is a defense that arises because the defendant is not blameworthy for having acted in a way that would otherwise be criminal.

For example, if someone commits a crime because they were forced to do so under threat of harm, they may have a legal excuse of duress. Similarly, if someone commits a crime because they were tricked into doing so by law enforcement, they may have a legal excuse of entrapment. Other traditional excuses include infancy, insanity, and involuntary intoxication.

These examples illustrate how a legal excuse can be used to defend against criminal charges. If a defendant can prove that they had a valid legal excuse for their actions, they may be found not guilty or have their charges reduced.