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.
>>samatm+os
Among American sailors you will find "reef knot" dominates: it is the knot used to "reef" or diminish a sail's useful area. Among Boy Scouts (and no offense intended here) you will find the term "square knot" dominates.