Rain is described as water falling in drops condensed from vapor in the atmosphere. It is a liquid precipitation, as opposed to non-liquid kinds of precipitation such as snow, hail and sleet.
How does rain form?
When the sun shines onto the rivers and seas, the water evaporates. The water vapor that has evaporated condenses into cloud droplets in the cooler atmosphere. Many of these droplets form clouds. Also, water under heat, turns to an air form of water. When all this evaporated water adds up, it turns into a cloud. When enough water molecules with the clouds form together, they become too heavy for the upward flowing air to keep them in the cloud. These droplets then fall back down to earth as precipitation, and rain is the most common form of this.