The underscore _ is the character with ASCII value 95. On the standard US 101/102 computer keyboard it shares a key with the hyphen on the top row, to the right of the 0 key.

It is a character left over from the typewriter. Prior to the advent of word processing, using the underscore character was the only method of underlining words. To produce an underlined word, the word was typed, the typewriter carriage was then moved back to the beginning of the word and the word was overtyped with the underscore character.

It is used as a diacritic mark in some African and Native American languages. The underscore is sometimes used as an underdot (Unicode: COMBINING DOT BELOW) in romanized Arabic and Hebrew.

It is also often used instead of a space in computer operating systems, file names, and in World Wide Web URLs.

Some computer applications will automatically underline text surrounded by underscores: _underlined_ will render underlined. It is also conventionally used in this fashion on Usenet, an ASCII-only medium, to indicate underlining.

However, Microsoft Word changes text input between underscores to italics.

It is not a dash, and should not be used as such (although an apparent convention for text news wires is to use an underscore when a em-dash or en-dash is desired, or when other non-standard characters such as bullets would be appropriate). A series of underscores (like _________) may be used to create a blank to be filled in on a form. It is also sometimes used to create a horizontal line, if no other method is available.