A boat used for Kayaking. There are whitewater kayaks and flatwater kayaks. The whitewater ones are typically shorter so as to be easier to turn. The flatwater ones are longer so that they can go faster with less effort, and will hold a heading more easily. Whitewater kayaks are for use in flowing rivers. Flatwater kayaks are for use on lakes and seas and oceans. All that flatwater really means is 'not a river'.