This funny little symbol looks like a spider and attracts a lot of attention. On this continent we often call it the pound sign or the number sign, in the UK it is called the hash or sometimes the square (but never pound, this is their pound symbol £), in Singapore and Malaysia it is called the hex key, in China it is often called cross or jĭng as it looks like the character for water well (井), and Bell Laboratories has dubbed this the octothorpe since about 1968. It also goes by crosshatch, crunch, grid, hak, oof, pig-pen, punch mark, scratch mark, tictactoe and more.
In programming, this symbol is used for everything from a comment to a preprocessor directive and in editing it is used for a space. It is also used in mathematics and scrabble and chess and even in medicine (as shorthand for a fracture).
Regardless of what it’s called and who is using it, everyone should be careful to distinguish it from the musical sharp symbol (♯).
What a versitile symbol.