Grille


A grille or grill is an opening of several slits side-by-side in a wall, metal sheet or another barrier, usually to allow air or water to enter and/or leave and prevent larger objects from going in or out.
A similar definition is "a French term for an enclosure in either iron or bronze."

Register vs. grille

In heating, cooling, ventilation, or a combination thereof, a grille is a perforated cover for an air duct. Grilles sometimes have louvers which allow the flow of air to be directed.
A register differs from a grille in that a damper is included. However, in practice, the terms "grille", "register", and "return" are often used interchangeably, and care must be taken to determine the meaning of the term used.