A tether is a cord, fixture, or flexible attachment that anchors something movable to a reference point which may be fixed or moving. There are a number of applications for tethers: balloons, kites, tethered wind-energy conversion systems, anchors, tethered water-flow energy conversion systems, towing, animal constraint, spaceflight, and power-kiting. Also, tethering to prevent theft of an object like a computer at a school or library is now commonly seen.