窗或窗户，在建筑学上是指墙或屋顶上建造的洞口，用以使光线或空气进入室内。事实上窗和户的本意分别指窗和门，在现代汉语中窗户则单指窗。

“窗”本作“囱”（“囱”为俗字），即在墙上留个洞，框内的是窗棂，可以透光，也可以出烟，后加“穴”字头构成形声字。《说文》说：“在墙曰牅，在屋曰囱。窗，或从穴。”

A window is an opening in a wall, door, roof or vehicle that allows the passage of light and, if not closed or sealed, air and sound.

Modern windows are usually glazed or covered in some other transparent or translucent material. Windows are held in place by frames. Many glazed windows may be opened, to allow ventilation, or closed, to exclude inclement weather. Windows often have a latch or similar mechanism to lock the window shut.