Freefall is a scientific term for any body of mass currently in a state such that the only force acting upon it is the force of gravity. It is also popularly used as a skydiving term, meaning the time between exiting an aircraft and deploying a parachute. Additionally, in at least one instance that I know of, it is the name of an attraction at an amusement park.
Because we do not feel the force of gravity directly, freefall is the only time we can feel as if there are no external forces acting on us whatsoever. At all other times when we are upon the surface of the earth, something (usually the ground, or perhaps a chair) is pushing up against us, holding us away from the center of the planet. Because we are constantly exposed to this upward (really outward) force, freefall can take some getting used to.
Although skydiving is a quite popular approximation, it isn't technically freefall due to the overwhelming amount of rushing air causing an upward force. Roller coasters and the like can also allow you to ape the sensation of feeling nothing at all. Other choices for the freefall-seeking adventurer include NASA's vomit comet or becoming an astronaut; a spacecraft traveling in orbit around a planet is in freefall, since the vessel is constantly being pulled down towards the planet and just as constantly missing it due to forward velocity.