The cryosphere is the part of the Earth’s surface where water is in solid form, including sea ice, lake ice, river ice, snow cover, glaciers, ice caps and ice sheets, and frozen ground (which includes permafrost). It often overlaps with the hydrosphere, the water on, under and over the surface of the Earth. The cryosphere is an important part of the global climate system. It influences surface energy, clouds, precipitation, hydrology, and the way both air and water move about in the atmosphere and oceans. The cryosphere is important to understanding how the climate of Earth works and how it affects global climate. The word "cyrosphere" comes from the Greek word "cryo" meaning "cold" or "to cold".