A ground-effect vehicle (GEV), ekranoplan (from Russian: экранопла́н "screenglider"), wing-in-ground-effect (WIGE or WIG), ground-effect craft/machine (GEM), wingship, flarecraft, or surface effect vehicle, is a hybrid surface vehicle/aircraft that makes use of wings to generate minimal lift and ground effect, to reduce aerodynamic drag. Ground effect is the interaction between a moving wing and a stationary surface below it.

Typically, a GEV will glide just above a relatively level surface. Some vehicles can operate over any flat area such as a lake or flat plains.

Technically, GEVs do not include racecars that utilize ground-effect, for increasing downforce, as such vehicles are intended to remain in direct contact with a racetrack.

In aircraft, the ground effect is the reduced aerodynamic drag that an aircraft's wings generate when they are close to a surface (land or water).

The principal benefit of operating in ground effect is to reduce its lift-induced drag. The closer the wing operates to a surface such as the ground ("in ground effect"), the less drag it experiences. When an aircraft enters ground effect, the surface pushes back against the downwash, which reduces its drag.

During takeoff, ground effect can cause an aircraft to "float" while accelerating towards the climb speed, reducing friction.

Any airfoil passing through air increases air pressure on the underside, while decreasing pressure on the upper side, which generates lift. The high and low pressures are maintained until they flow off the ends of the wings, where they form vortices that are the major source of lift-induced drag—normally a significant portion of the total drag.

In GEV, the angle of attack is the angle between its chordline (a straight line from the leading edge to the trailing edge) and the ground. On takeoff, airplanes pitch their noses up to increase the angle of attack to reach the ideal of 12-20 degrees (depending on wing design and other factors).