Kayak is a small, relatively narrow, human-powered boat primarily designed to be manually propelled by means of a double blade paddle. The traditional kayak has a covered deck and one or more cockpits, each seating one paddler. Their cockpit is sometimes covered by a spraydeck (or "skirt") that prevents the entry of water from waves or spray and makes it possible for suitably skilled kayakers, to roll the kayak: that is, to capsize and right it without it filling with water or ejecting the paddler. (http://en.wikipedia.org/wiki/Kayak, 2013)
Take a look at our guide Choosing the right kayak.