The Ashley stopper knot is a simple to tie stopper knot that is pretty bulky so it won't slip to bigger holes. The Ashley stopper knot has several purposes. It can be used to prevent a rope from slipping through a hole. But it can also be used to prevent a rope from slipping through another knot.
The knot is invented by Clifford W.Ashley the writer of the famous Ashley's book of knots, hence the name.
The Ashley stopper knot is also know as the Oysterman's stopper knot.