The story
From the idea of the executive's holding the bill in a coat pocket.
Etymology from Wiktionary, CC BY-SA 4.0.
pocket veto
Today it means: A (de facto) veto of a bill by the US President by restricting Congressional action on the bill, as, figuratively, by carrying the bill in his pocket until the deadline for signing it has passed, at a time when Congress has adjourned. Full definition →