Geothermal activity refers to the heat that comes from the Earth's interior. This heat can be found in various forms, such as hot springs, geysers, and volcanic eruptions. The Earth's core generates this heat, which can rise to the surface through cracks and fissures in the crust. Areas with significant geothermal activity, like the Yellowstone National Park in the United States, often showcase unique geological features. These regions can harness geothermal energy, a renewable resource used for heating and electricity generation, making it an important aspect of sustainable energy development.