Full form of OTEC is:
A. Ocean thermal energy conversion power plant.
B. Ocean thermal consumer energy power plant.
C. Ocean current thermal energy cycle.
D. Ocean current thermal electric current.

Hint: It is one of the available renewable energy sources. It can operate with a very high capacitor factor and so can operate in base load mode. It is the process that produces electricity by using the temperature between deep cold ocean water and warm tropical surface water.

Complete answer:
In 1881, Jacques Arsene d'Arsonval, A French physicist, proposed the thermal energy of the ocean. Japan is the major contributor to the development of ocean thermal energy conversion technology.

The OTEC stands for ocean thermal energy conversion power plant.

It produces energy from temperature differences in ocean water. Basically it uses the ocean thermal gradient between a cooler deep and warmer shallow or surface seawater to run a heat engine and produce in the form of electricity.
It works on the principle of warm surface water with a temperature of $25^\circ {\text{C}}$, to vaporize the fluid which has a low boiling point, such as Ammonia. The vapors expand and spin the turbine to generate electricity. Here ammonia is used as working fluid because it has a low melting point, which when turned into gas, moves the steam into pressurized shafts that are used to drive turbines.

Note:
The maximum possible Carnot thermal efficiency of an ocean thermal energy conversion power system is about 7%. It has two biggest advantages, that it produces clean environmentally friendly renewable energy and produces energy all the time. Wind turbines work only when it is windy.