A terminator is a device that absorbs, transmits and reflects all the energy in a wave. One type of terminator is an overtopping device that uses a floating reservoir structure, typically with reflecting wings to focus the wave energy. Water is lead to a plateau above the natural sea level. The collected water is then lead through turbines generating electricity.
As waves arrive, they overtop the device and are restrained in the reservoir. The head of the collected water as it flows back out to sea turns conventional low-head hydro turbines, and the turbines are coupled to generators to produce electricity. 

 

Illustration: As waves arrive, they overtop the device and are restrained in the reservoir.

One example of the overtopping terminator device is the Wave Dragon. Source: Wave Dragon.