A window is an opening within the wall of the building, in the car etc., to let air and light in. It is usually filled with the sheet of glass. They can be many different shapes, including rectangular, square, circular, or irregular shapes.

A window of the house in England

In the operating system similar to Microsoft Windows or Mac OS, the window is the part of the screen that displays some data to the user. There are many different windows, for example web browser.