I think you might be underestimating what it means to be fluent in a language. The most important criterion in my opinion is whether you are able to freely speak in that language without doing any on the fly translating.
Geothermal energy is thermal energy within the Earth due to the movement of the Earth's particles. Most of this geothermal energy is contained within the core of the Earth. This geothermal energy is renewable energy as it is energy derived from a natural resource and it can be replenished.
Geothermal heating is the direct use of geothermal energy for heating some applications. Humans have taken advantage of geothermal heat this way since the Paleolithic era. Approximately seventy countries made direct use of a total of 270 PJ of geothermal heating in 2004. As of 2007, 28 GW of geothermal heating capacity is installed around the world, satisfying 0.07% of global primary energy consumption.