Here's a breakdown:

* Geo: Comes from the Greek word "ge", meaning "earth".

* Thermal: Relates to heat or temperature.

Therefore, "geo-thermal" means "earth heat".

It's used to describe:

* Geothermal energy: This is energy derived from the heat within the Earth's crust. It can be used for electricity generation, heating, and cooling.

* Geothermal features: These are naturally occurring phenomena that arise from the Earth's internal heat, such as hot springs, geysers, and volcanoes.

In essence, "geo-thermal" encompasses all things related to the heat originating from within the Earth.