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'.