According to the International Civil Aviation Organization (ICAO), a runway is a "defined rectangular area on a land aerodrome prepared for the landing and takeoff of aircraft". Runways may be a man-made surface or a natural surface. Runways, as well as taxiways and ramps, are sometimes referred to as "tarmac", though very few runways are built using tarmac. Runways made of water for seaplanes are generally referred to as waterways. Runway lengths are now commonly given in meters worldwide, except in North America where feet are commonly used.
