1. Video containing information or allowing information entry, keyed into the video monitor output for viewing on the monitor CRT. A window dub is a copy of a videotape with time code numbers keyed into the picture. 2. A video test signal consisting of a pulse and bar. When viewed on a monitor, the window signal produces a large white square in the center of the picture. 3. A graphical user interface that presents icons and tools for manipulating a software application. Most applications have multiple windows that serve different purposes.