Geothermal energy is a renewable energy obtained through the use of natural heat from the interior of the earth that is transmitted through the hot rock bodies or reservoirs by conduction and convection, where fluid and rock interaction processes occur, giving rise to geothermal systems.

The term "geothermal" comes from the Greek geo "Earth", and thermos "heat"; literally "heat" of the Earth. The interior of the Earth is hot and the temperature increases with depth. The deep layers are at high temperatures and, often, at that depth there are water tables in which water is heated: when ascending, hot water or steam produce surface manifestations, such as geysers or hot springs, used for bathrooms since Roman times. Currently, progress in drilling and pumping methods allows geothermal energy to be exploited in many parts of the world.