A localized geological environment in which circulating steam, or hot water, carries some of the Earth's natural internal heat flow close enough to the surface to be utilized for productive human use: A geothermal system is one kind of technological system that makes use of this heat as an energy source, such as to power an electrical power plant, or to heat or to cool a building.

A system used to extract heat from the less productive margins of existing geothermal fields, or from entirely new fields that are lacking sufficient production capacity under current conditions by utilizing a combination of hydraulic, thermal, and chemical processes; such as, rock fracturing, water injection, or water circulation.