Final answer:
The water cycle is defined by the continuous movement of water through its states—liquid, vapor, and ice—driven by solar energy and gravity, involving processes like evaporation, condensation, and precipitation.
Step-by-step explanation:
The defining characteristic of the water cycle, also known as the hydrologic cycle, is the continuous movement of water on, above, and below the surface of the Earth. This cycle involves various processes such as evaporation/sublimation, condensation/precipitation, subsurface water flow, surface runoff/snowmelt, and streamflow. Driven by solar energy and gravity, water in the cycle changes states between liquid, vapor, and ice. These transformations allow water to travel from the oceans to the atmosphere, form clouds, and then return to Earth as precipitation (rain or snow), where it either flows over the surface or percolates into the ground feeding groundwater storage systems.