One megawatt is the unit of power equal to 1,000 kilowatts. MW(th) denotes the thermal power of a generating station, that is, the rate at which heat is produced (by combustion if it is a conventional thermal plant, by fission in the reactor core if it is a nuclear reactor). MW(e) denotes the electrical power output of the station and is only a fraction of the thermal power - typically about 30% for a heavy water reactor and up to 40% for a modern fossil-fuel-fired station. The latter radio - MW(e)/MW(th) - is called the thermal efficiency of the power station.
A megawatt is a million watts, sufficient power to light 10,000 100-watt bulbs, or enough electricity for around 3,000 households. The watt is a unit of power, equal to one joule per second. Sometimes the unit MWe, or "megawatt electric" is used to distinguish the electrical power produced by a plant from the larger amount of heat (MWt, or megawatt thermal) required to make that electricity, due to the inherent limitation on the efficiency of converting heat to electricity.
1,000,000 watts or 1,000 kilowatts. Abbreviated MW