From Wired:

Developed in the 1960s, the Harrier is marvelous for its ability to hover like a helicopter. The jet engine pumps air through four nozzles, two on each side of the fuselage, right under the wings. They rotate to propel the plane forward or straight up, allowing for very short takeoffs and vertical landings, and unchaining the plane from the need for long runways. The Harrier can operate out of clearings in the jungle (think Vietnam), a landing dock designed for helicopters, or downtown Miami (where Arnold Schwarzenegger uses one to win the day in “True Lies”).