This strange acronym stands for Vertical and/or Short Take-Off and Landing aircraft. It actually describes a system whereby the aircraft is designed to take-off and land on very short runways, and air strips. The technology has been developed in the 1950s, and pushed today to aircrafts capable of hovering to take off and land. Helicopters are not considered under the V/STOL classification as the classification is only used for airplanes, aircraft that achieve lift in forward flight by planing the air, thereby achieving speed and fuel efficiency that is typically greater than helicopters are capable of. Most V/STOL aircraft types were experiments or outright failures from the 1950s to 1970s. V/STOL aircraft types that have been produced in large numbers include the Harrier, Yak-38 Forger and V-22 Osprey. V/STOL was developed to allow fast jets to be operated from clearings in forests, from very short runways, and from small aircraft carriers that would previously only have been able to carry helicopters. The main advantage of V/STOL aircraft is closer basing to the enemy, which reduces response time and tanker support requirements. In the case of the Falklands War, it also permitted high performance fighter air cover and ground attack without a large aircraft carrier equipped with a catapult. A rolling takeoff, sometimes with a ramp (ski-jump), reduces the amount of thrust required to lift an aircraft from the ground (compared with vertical takeoff), and hence increases the payload and range that can be achieved for a given thrust. For instance, the Harrier is incapable of taking off vertically with a full weapons and fuel load. Hence V/STOL aircraft generally use a runway if it is available. I.e. short takeoff and vertical landing (STOVL) or conventional takeoff and landing (CTOL) operation is preferred to VTOL operation.
Check out the latest F-35 jet fighter landing on the aircraft carrier and demonstrating perfectly what a VSTOL aircraft is.