In computing, the term button (sometimes known as a command button or push button) refers to any graphical control element that provides the user a simple way to trigger an event, like searching for a query at a search engine, or to interact with dialog boxes, like confirming an action.

In computing, the term button (sometimes known as a command button or push button) refers to any graphical control element that provides the user a simple way to trigger an event, like searching for a query at a search engine, or to interact with dialog boxes, like confirming an action.

A typical button is a rectangle or rounded rectangle, wider than it is tall, with a descriptive caption in its center. The most common method of pressing a button is clicking it with a pointer controlled by a mouse, but other input such as keystrokes can be used to execute the command of a button.

A button is not however always restricted to a rectangular shape. The sole requirement of button interaction is that the user can execute a command by a click action. Thus pictures and background areas can be programmed as buttons. When pressed, in addition to performing a predetermined task, buttons often undergo a graphical change to mimic a mechanical button being depressed.

You can read more about it at: Button (computing) - Wiki.