Tab key (abbreviation of tabulator key or tabular key) on a keyboard is used to advance the cursor to the next tab stop.

The word tab derives from the word tabulate, which means "to arrange data in a tabular, or table, form." When a person wanted to type a table (of numbers or text) on a typewriter, there was a lot of time-consuming and repetitive use of the space bar and backspace key. To simplify this, a horizontal bar was placed in the mechanism with a moveable lever stop for every position across the page. Initially these were set by hand, but later tab set and tab clear keys were added. When the tab key was depressed, the carriage advanced to the next tab stop. These were set to correspond to the particular column locations of the table, hence tab, being worked on. The tab mechanism also came into its own as a rapid and consistent way of uniformly indenting the first line of each paragraph.

In many programming languages the escape code \t can be used to insert a tab.

In modern applications, the Tab key rarely has the effect of inserting the Tab character. In word processor applications, the Tab key typically moves the cursor to the next tab stop. In most other graphical applications, the Tab key will shift the focus to the next control or widget.