1Short for (a) tabulate, i.e. to lay out data; (b) tabulation character, a control character used when laying out data to control the movement of a print or display mechanism. Most keyboards have a tab key, which may initiate the tabulation function or may be used for other control purposes.
2 A feature of many graphical interfaces where the user may select one of several optional screens by clicking on the tab. The term derives from card -nindexes where a small extension of the card allows easy identification of the required card.