(1) Short for tabulator; on typewriter keyboards, a key that allows you set automatic stops (tab stops) or margins for columns, as in a table of figures. (2) An ASCII character that commands a device such as a printer to start printing at a preset location (called a tab stop). There are two such characters: horizontal tab (hex 09) and vertical tab (hex 0B). The horizontal tab character gives the same action as pressing the tab key on a typewriter.