Question

what is geothermal energy ?

Answer 1

Geothermal energy is thermal energy generated and stored in the Earth. Thermal energy is the energy that determines the temperature of matter. The geothermal energy of the Earth's crust originates from the original formation of the planet and from radioactive decay of materials (in currently uncertain[1] but possibly roughly equal[2]proportions). The geothermal gradient, which is the difference in temperature between the core of the planet and its surface, drives a continuous conduction of thermal energy in the form of heat from the core to the surface. The adjective geothermal originates from the Greek roots γη (ge), meaning earth, and θερμος (thermos), meaning hot.

Answer 2

Here is your answer !!
Geothermal energy is a thermal energy (an energy which shows the temperature of earth) which is generated and stored in the earth.
In other words, we can say that Geothermal energy is the energy obtained by tapping underground reservoirs of heat, usually near volcanoes or other hot spots on the surface of the Earth. 

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