Geothermal energy is obtained from the hot areas under the surface of the earth in the form of hot water or steam extracted from reservoirs in the earth's crust. Water or steam extracted from geothermal reservoirs can be used for geothermal heat pumps, water heating, or electricity generation. Lower temperature, shallow ground, geothermal resources are used by geothermal heat pumps to heat and cool buildings

Additional Resources
http://www.geothermal.org/what.html