Definition of Windowing environment

From a programmer's point of view, a windowing system implements graphical primitives such as rendering fonts or drawing a line on the screen, effectively providing an abstraction of the graphics hardware.

A windowing system enables the computer user to work with several programs at the same time. Each program runs in its own window, which is an area of the screen, typically a rectangle. Most windowing systems allow windows to overlap, and provide means for the user to perform standard operations such as moving/resizing a window, sending a window to the foreground/background and minimizing/maximizing a window.