Rain is falling moisture from the atmosphere.Rain is the most common type of Precipitation.It is made when small droplet of water join together in clouds to form bigger droplets of water that fall out of the clouds.When rain starts out of the clouds it is usualy about 5mm (0.02inches) around.When rain is falling through the air it gathers up into bigger rain drops like the size that hit your house. Sometimes rain comes down hard and fast and sometimes it just comes down slow and light the only thing that is different is how much water the clouds have collected.