Sailing speed units are typically measured in knots, which is a unit of speed equal to one nautical mile per hour. Knots are used to measure the speed of boats and ships, as well as the speed of wind and currents. The term 'KNOT' originates from the Middle English word 'knotte, ' which means to tie or bind. Knots are also used to measure the speed of aircraft, although they are usually referred to as nautical miles per hour.