Coal is called fossil fuel because it is the type of energy source which is formed from the remnant of dead plants and animals which decayed in the presence of high pressure and temperature inside the earth surface.
Fossil fuels get their name because they are literally made from fossils — dead organisms (mostly plants) that didn't decay because they were squashed under water or mud with no oxygen. ... The plants that were buried deep at sea were converted to oil and gas, and those buried in swamps became coal.Coal, oil, and natural gas are fossil fuels formed over time from the remains of living organisms. In the United States, they supply most of our energy needs, including roughly two-thirds of US electricity generation.
Coal is primarily used as fuel to generate electric power in the United States. In coal-fired power plants, bituminous coal, subbituminous coal, or lignite is burned. The heat produced by the combustion of the coal is used to convert water into high-pressure steam, which drives a turbine, which produces electricity.