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.
>>jet_32+Sx
Scouts, but not in the US, was where I learnt it as "reef knot", it's pretty much the go-to knot there, to the point where I recall it making up part of a lot of designs on badges and such.
>>eythia+Gi1
It was a reef knot in the Scouts in the UK also. And a granny knot was a reef know where the sequence was repeated (RoL/RoL or LoR/LoR rather than LoR/RoL IIRC.)