Weightlessness is a phenomenon experienced by people during free-fall. Although the term zero gravity is often used as a synonym, weightlessness in orbit is not the result of the force of gravity being eliminated or even significantly reduced (in fact, the force of the Earth's gravity at an altitude of 100 km is only 3% less than at the Earth’s surface). Weightlessness typically occurs when an object or person is falling freely, in orbit, in deep space (far from a planet, star, or other massive body), in an airplane following a particular parabolic flight path (e.g., the “Vomit Comet”), or in one of several other more unusual situations.