Geothermal means “to do with the heat that is already inside the Earth.” Deep underground the rock stays hot. Water down there can come up hot by itself, or people can send water down to pick that heat up and bring it back. We use the word most for power and for hot springs: geothermal energy, a geothermal plant, geothermal water. It is a science and news word, not a kitchen word. People sometimes stretch it to mean any natural hot water, but strictly the heat has to come from the Earth itself, not from the sun warming a pool, and not from a boiler. A kettle is hot; it is not geothermal.

地熱的；地熱（地熱發電、地熱溫泉）