Economy-class syndrome refers to the medical condition that affects people who sit in the economy class of an airplane for an extended period. This condition is caused by prolonged sitting in a cramped position that can lead to blood clots in the legs. In medical terms, this condition is known as deep vein thrombosis. Other synonyms for economy-class syndrome include travel thrombosis, economy class syndrome, thrombophlebitis, venous thromboembolism, and airplane thrombosis. All these conditions refer to the same medical problem of blood clots that can be caused by sitting for too long in a small space while on a long-distance flight.