Restricted airspace refers to an area in which certain flight operations are restricted or prohibited. This type of airspace is typically designated by a specific altitude, distance from an airport, or other criteria that make it unsafe for general aviation traffic. Restricted airspace can be used for various purposes such as military training exercises, testing and evaluation activities, or to provide additional safety margins around certain areas of high density traffic. Pilots must receive proper authorization and clearance from Air Traffic Control before entering restricted airspace in order to ensure the safety of all aircraft operating within that area.