Geothermal power means using heat from the earth to make electricity. In the United Kingdom, there are hot rocks underground that can be used to make geothermal power.
First, people drill a hole into the ground to reach the hot rocks. Then, they pump water into the hole to make steam. The steam comes back up to the surface and turns a turbine, which makes electricity.
The United Kingdom has some places where geothermal power could be used, but it is not used very much yet because it can be expensive to drill the holes and build the power plant. However, some people think that geothermal power could be good for the environment because it does not make pollution like other kinds of power.