[1] Such an act, even if innocent per se, can potentially be used as evidence against someone during a trial to show participation in a crime.
The term is more particularly employed in cases of treason, which must be demonstrated by some overt or open act in some jurisdictions.
[1][3] This rule was enacted in the law of England (see the Treason Act 1547), and was later adopted by the United States in Article III, Section 3 of the United States Constitution, which provides that "No Person shall be convicted of Treason unless on the Testimony of two Witnesses to the same overt Act, or on Confession in open Court.
"[4] In Cramer v. United States, the Supreme Court ruled that "every act, movement, deed, and word of the defendant charged to constitute treason must be supported by the testimony of two witnesses.
[6] In some jurisdictions, a defendant cannot be convicted of criminal conspiracy unless an overt act is proved.