A mechanism for setting automatic stops or margins in order to line up text or items in columns. Also a key on the keyboard that moves the cursor or pointer to the next tab stop.

The tab function in a word processor works much like the tab function on a typewriter. Tab stops can be set in the ruler at the top of the page. When the tab key is pressed, the cursor will move to the next tab location. This allows the user to indent paragraphs and lists.