Precipitation is the process by which condensed water droplets in the atmosphere combine and become heavy enough to fall to the Earth's surface as rain, snow, sleet, or hail.
When the cloud's capacity to hold moisture is exceeded, the water droplets or ice crystals coalesce and grow in size. When these droplets or crystals become heavy enough, gravity pulls them down to the Earth's surface, leading to precipitation.
The type of precipitation (rain, snow, sleet, hail, or drizzle) depends on the temperature and atmospheric conditions.