While I was aware of the term "Reef knot", that knot is commonly, almost exclusively, called a "Square knot" in my (midwestern American) dialect of English.
Is this a British thing?
Reef, bowline, and figure-eight are the three knots you must be able to tie behind your back to pass a basic sailing class.
I will reiterate though, that the reef knot is called a square knot where I come from. Misnomer? I guess, that's what everyone calls it, an overhand stop knot is an overhand or just a "knot" actually.