Geothermal energy (geo = earth & therme = heat) is transferring heat energy from underground.
Below the earth’s surface there are vast amounts of free untapped energy that rises from the Earth’s core, where it can sometimes be transferred into our homes, factories or offices for our own use.
In some parts of the world the heat rises quite close to the surface. Water can be pumped down up to 2 miles deep, where very hot underground rocks boil the water to make steam. This is then brought back to the surface to run electrical generators.
Heat from the ground can also be used to heat homes.
Watch this video on how Iceland uses underground volcanoes to heat water, which generates electricity and also heats most of the country's homes.