The_Underscore

The underscore ( _ ) is the character with ASCII value 95. On the standard US or UK 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 also often used instead of a space in computer operating systems, filenames, e-mail addresses, 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 to indicate emphasis, and can be used in other ASCII-only media (E-mail, IRC, Instant Messaging) for this purpose. When the underscore is used for emphasis in this fashion, it is usually interpreted as indicating that the enclosed text is underlined or italicised, as opposed to bold.
Underscore 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 an 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.