A pocket veto occurs when a bill fails to become law because the president does not sign the bill and cannot return the bill to Congress within a 10-day period because Congress is not in session. Article 1, Section 7 of the U.S. Constitution states:
If any Bill shall not be returned by the President within ten days (Sundays excepted) after it shall have been presented to him, the same shall be a Law, in like manner as if he had signed it, unless the Congress by their Adjournment prevent its return, in which case it shall not be a Law.