The watt is named after James Watt  for his contributions to the development of the steam engine, and was adopted by the Second Congress of the British Association for the Advancement of Science in 1889 and by the 11th Conférence Générale des Poids et Mesures  in 1960.
A watt is a unit of power or the amount of energy per unit time.
When paired with a unit of time the term watt is used for expressing energy consumption. For example, a kilowatt hour, is the amount of energy expended by a one kilowatt device over the course of one hour; it equals 3.6 megajoules (1 hour = 3600 seconds). These units are often used in the context of power plants and home energy bills.
For the use of watts as a measurement of transmitter power in radio, see effective radiated power and nominal power.
Watt electrical (abbreviation: We) is a term that refers to power produced as electricity. SI prefixes can be used, for example megawatt electrical (MWe) and gigawatt electrical (GWe).
Watt thermal (abbreviation: Wt). This is a term that refers to thermal power produced. SI prefixes can be used, for example megawatt thermal (MWt) and gigawatt thermal (GWt). For example, a nuclear power plant might use a fission reactor to generate heat (thermal output) which creates steam to drive a turbine to generate electricity.
This SI unit is named after James Watt . As for all SI units whose names are derived from the proper name of a person, the first letter of its symbol is uppercase (W). But when an SI unit is spelled out, it should always be written in lowercase (watt), unless it begins a sentence or is the name "degrees Celsius".