What is the meaning of Louver?

A type of turret on the roof of certain medieval buildings designed to allow ventilation or the admission of light.

A series of sloping overlapping slats or boards which admit air and light but exclude rain etc.

Any of a system of slits, as in the hood of an automobile, for ventilation.

to drill a hole in a stone for the attachment of a wedge

Source: wiktionary.org