The water cycle is the process that links the movement of water through the environment. At it's simplest, the water cycle consists of three steps: evaporation, condensation, and precipitation.
Let's start with water that is on the ground (or in a body of water). As light energy heats that water, the individual water molecules absorb enough energy to break away from each other and begin rising into the atmosphere. That is evaporation. Those water molecules rise into the atmosphere and begin to cool. Once the temperature reaches the dew point, the air is said to be saturated (100% humidity), and condensation will occur. The water vapor will condense into either light weight water droplets or lightweight ice crystals. Most people call those things clouds. Condensation will continue until the condensed droplets are heavy enough to fall toward earth. Falling water is called precipitation, and it falls in a variety of forms. The most common would be rain, sleet, snow, and hail. The water cycle will then start over again.
Earlier I said that a three step water cycle was the simple version. A five step version is much more accurate in describing the water cycle in its entirety. The fourth step is runoff. Water that is on earth's surface is not always stationary. It moves. It flows down hills and streets. It moves along streams and rivers. There are underground aquifers. If the water cycle is defined as a process that moves water through the environment, runoff is a key piece.
The fifth piece of the water cycle is called transpiration. A lot of water is held within plants. They need it to perform photosynthesis. The plants also need carbon dioxide. Plants get the gas by opening up little doors on their leaves called stoma. It's a great system for gas exchange, but water vapor is also released through the stoma. Transpiration is a special kind of evaporation. It's water entering the atmosphere from plant life.
Together transpiration, runoff, precipitation, evaporation, and condensation make up the water cycle.