What is the term for the president's power to kill a bill by not signing it when Congress is not in session?

The term for the president's power to kill a bill by not signing it when Congress is not in session is known as a pocket veto. This mechanism allows the president to effectively prevent a bill from becoming law without issuing a formal veto, specifically when Congress adjourns within the ten days allotted for the president to sign or veto legislation. As a result, if no action is taken, the bill does not become law, illustrating the significant influence the president has over legislation, particularly during the congressional recess.

The other terms do not accurately describe this specific presidential power. A line-item veto, for example, refers to the authority to reject specific provisions of a bill without vetoing the entire piece of legislation. An executive order is a directive issued by the president to manage operations within the federal government, not a way to veto legislation. A veto override occurs when Congress votes to pass a bill despite the president's veto, which is a different legislative process altogether.