If you ever search for window in Wikipedia, it says " A window is an opening in a wall or roof of a building, etc., to let air and light in. It is usually filled with a sheet of glass. There can be many different shapes or irregular shapes. Windows are usually transparent so that people can see through them. " As one of windows with regular shapes, slim modern window features a slimmer frame. The common frame width is about 4.53 inches (approx. 115mm) while slim window's frame is about 2.95 inches (approx75mm). That means it reduces about 1.58 inches (approx. 40mm), which should be 35% slimmer than regular frame. This is how the window gets its name with slim.