Backslash

The backslash \ is a typographical mark used mainly in computing and mathematics. It is the mirror image of the common slash ('solidus'), /. It is a relatively recent mark, first documented in the 1930s. It is sometimes called a hack, whack, escape (from C/UNIX), reverse slash, slosh, backslant, backwhack, bash, reverse slant, reverse solidus, and reversed virgule.