1. An area on a screen that when activated by means of a pointing device or predetermined key sequence causes an action to be initiated. Buttons can be any shape or size and need not be visible. The commonest form is a small rectangular area shaded to give the appearance of protruding slightly from the screen and labelled with text that indicates its function (‘close’, ‘ok’, ‘print’, etc.) or with an icon. When the button is activated or ‘pressed’, its appearance will normally change so that it appears recessed. A horizontal or vertical row of buttons is called a button bar.

2. On a mouse (or similar device), a switch that a user presses to initiate a specific function (see click).