Backslash

A backslash, \, is a punctuation mark used chiefly in computing. Sometimes called a reversed solidus, it is the mirror image of the common solidus or slash mark.

On Unix systems, and in Unix-affiliated programming languages such as C and Perl, the backslash is used to indicate that the character following it should be treated specially. It is sometimes referred to as the escape character, though this risks confusion with the character generated by the Esc key.

On DOS and Microsoft Windows computer systems, the backslash is used as a delimiter for directory names in file paths. This is in contrast to the use of the slash for this purpose on Unix and other systems. The backslash was chosen for path delimiter because in an early version -- which did not support directories and thus had no need for a path delimiter -- the slash was used to introduce command-line options.

In the TeX typesetting system, the backslash begins a markup tag.