In earlier days of text editors that worked with text modeCRTdisplays, when a paragraph had to be justified, this was achieved by means of inserting extra soft spaces at whitespaces. The soft spaces were so called because they could be "compressed" away during further editing. By contrast, ordinary spaces were called hard or incompressible spaces.
Also, in some older text editors, the hard spaces were both non-expandable—i.e., no soft spaces could be added to them—and non-breaking ones.
In many term programs and game parsers, a hard space was a special kind of field delimiter, against which a filename could be examined or listed, or a semantic thought or consideration could be interpreted.
In the Commodore directory system, a hard space usually terminated the spelling of a filename, and was replaced with a quotation mark when listed to the user.