In computing, a window is a portion of a computer screen, usually rectangular in shape, showing the output of and allowing input for one of a number of simultaneously running computer processes. The size and position can normally be adjusted, for example covering the whole screen, or half the screen, allowing another non-overlapping window using the other half, etc. Windows are a popular feature (or widget) in several graphical user interfaces. The X Window System and Microsoft Windows are named after this feature.

In computer networking, a window is the amount of data that can be transported before a source must give an acknowledgement (ACK) to the sender.

See also Window manager.