A hangar is a closed structure to hold aircraft and/or spacecraft in protective storage. Most hangars are built of metal, but wood and concrete are other materials used. The word hangar comes from a northern French dialect, and means "cattle pen."
Hangars protect aircraft from weather and ultraviolet light. Hangars may be used as an enclosed repair shop or, in some cases, an assembly area. Additionally, hangars keep secret aircraft hidden from satellites or spyplanes.