A g-suit, or the more accurately named anti-g suit, is a flight suit worn by aviators and astronauts who are subject to high levels of acceleration force (g). It is designed to prevent a black-out and g-LOC (g-induced Loss Of Consciousness) caused by the blood pooling in the lower part of the body when under acceleration, thus depriving the brain of blood. Black-out and g-LOC has caused a number of fatal aircraft accidents.
Read more about G-suit: Operation, Design, History, Use in Prone Pilot Position Aircraft, Use in Military Aviation and In Space, Use in Red Bull Air Race