Wiktionary
insurance shot
n. (context shooting English) A second (or subsequent) shot fired at a downed animal to ensure it is dead.
Usage examples of "insurance shot".
He fired twice, the first shot in the chest and the second, an insurance shot, in the head.
A guy who uses a silenced small-calibre automatic for a neat head shot and an insurance shot is not the type of guy who then suddenly goes berserk and kicks the shit out of a corpse, right?