An amphibious vehicle (or simply amphibian), is a vehicle that is a means of transport, viable on land as well as on (or under) water. Amphibious vehicles include amphibious bicycles, ATVs, cars, buses, trucks, military vehicles, boats and hovercraft. Classic landing craft are not amphibious vehicles as they do not offer any real land transportation at all, although they are part of amphibious assault. Ground effect vehicles, such as Ekranoplans, will likely crash on any but the flattest of landmasses so are also not considered to be amphibious vehicles.
Text from Wikipedia