A bay window is a window space projecting outward from the main walls of a building and forming a bay in a room, either square or polygonal in plan. While most bay windows protrude from a building, some bay windows are level with the exterior and are built into the interior of a room. The angles most commonly used on the inside corners of the bay are 90, 135 and 150 degrees.
Bay windows are often associated with Victorian architecture and were a part of the Gothic Revival style. The windows are commonly used to provide the illusion of a larger room. They are used to increase the flow of natural light into a building as well as provide views of the outside that would be unavailable with an ordinary window.