Wave energy would be any type of machine that uses the motion of individual waves or swells, rather than tides.
There is a wide range of ideas, most are at small scale, early stage, and no winner has emerged the same way that wind energy has seen the 3 bladed turbine win out.
Wave energy devices exist using almost any type of power take off mechanism - direct drive electric generators, linear generators, compressed air, and hydraulic actuators. Some may even use propellers in water but that's not as common since direction is always changing.
