窗 (chuāng) is a concise, written-style word for 'window', often used in compounds (e.g., 车窗 'car window'). It's more formal than 窗户 (chuāng hu), which is the everyday spoken word for a physical window in a room. 窗口 (chuāng kǒu) refers to a service window or computer window, not a building's window.