A spinnaker is a special type of sail that is designed specifically for sailing off the wind from a reaching course to a downwind, i.e. with the wind 90°–180° off bow. The spinnaker fills with wind and balloons out in front of the boat when it is deployed, called flying. It is constructed of lightweight fabric, usually nylon, and is often brightly coloured. It may be optimised for a particular range of wind angles, as either a reaching or a running spinnaker, by the shaping of the panels and seams. Some types of spinnaker can be carried by the side of the boat, but still in front of the mast. This is called "Flying a shy spinnaker", and is used for reaching [see below].
The spinnaker is often called a kite, or a chute (as in cruising chute) because it somewhat resembles a parachute in both construction and appearance. This should not be confused with the spinnaker chute which is a hull fitting sometimes used for launching and recovering the spinnaker. A purported etymology has the first boat to carry this sail being a Cowes yacht named Sphinx, from which "Sphinx's Acre" and eventually "Spinnaker".