The process by which water changes into vapor is called evaporation. This transformation occurs when water molecules at the surface gain enough energy, usually from heat, to transition from a liquid state to a gaseous state. Evaporation is a critical part of the water cycle, where water in lakes, rivers, and oceans evaporates into the atmosphere, contributing to cloud formation and precipitation. Factors such as temperature, surface area, and humidity influence the rate of evaporation. It is a natural process that plays a vital role in maintaining the balance of ecosystems and weather patterns.