The water cycle describes the continuous movement of water on, above, and below the surface of the Earth. It involves stages such as evaporation, transpiration, condensation, and precipitation. Evaporation occurs when water is heated by the sun and changes from a liquid to vapor, transpiration is when water vapor is released from plants, condensation happens when water vapor condenses into liquid water in the atmosphere forming clouds, and precipitation occurs when clouds become too heavy and water falls back to Earth as rain, snow, or hail. The water cycle is crucial because it recycles the Earth's water supply and allows water to reach organisms and ecosystems.