What is "stopper knot"

n. (context nautical English) A knot placed in a rope either to prevent the end from fraying, or to prevent it from passing through a hole

n. a knot that prevents a rope from passing through a hole

A stopper knot (or simply stopper) is a knot that creates a fixed thicker point on an otherwise uniform thickness rope for the purpose of stopping the rope at that point from slipping out of a narrow passage. Stopper has three distinct meanings in the context of knotting and cordage.