Precipitation occurs when moisture in the atmosphere condenses and falls to the ground in the form of rain, snow, sleet, and hail. :lmao:
Seriously, like has been said, it is basically when you get too much of something dissolved in a solution. The solution can't hold anymore, so some of it "precipitates" out, usually in the form of a crystalline solid. Precipitation also can occur when two soluble compounds to react and form a solid in solution.
Try making rock candy and you can see precipitation first hand for yourself. Just google it if interested.