A vactrain (or vacuum tube train) is a very-high-speed rail transportation. It is a maglev (magnetic levitation) line using evacuated (air-less) or partly evacuated tubes or tunnels. The lack of air resistance permit vactrains to travel at very high speeds—up to 8,000 km/h, which is 5 times the speed of sound—using relatively little power. The system has been nicknamed World Metro