15.34. Glossary


A small picture that represents some functionality in a computer program. A user clicks on an icon to cause an action to be performed by a program.


A visual element of a graphical user interface that allows a user to give commands to an executing program. Example widgets include a command button, a slider bar, or a list box.

graphical user interface

A user interacts with a computer program by pointing, clicking, and dragging icons and widgets in a window on a computer screen.


An abbreviation for a “graphical user interface.”

event-driven programming

A program that only executes tasks when a user specially requests a task.

event loop

A built-in function of a GUI toolkit that “listens” for operating system events and then calls an appropriate event-handler for each event.


A function that processes an event. These functions are also called callback functions.

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