1. any or all forms of liquid or solid water particles that fall from the atmosphere and reach the earth's surface, including drizzle, rain, snow, snow pellets, snow grains, ice crystals, ice pellets, and hail —note the ratio of precipitation to evaporation is the most important factor in the distribution of vegetation zones 2. a measure of the quantity, expressed in inches, centimeters, or milliliters of liquid water depth, of the water substance that has fallen at a given location in a specified amount of time —see precipitation gauge, recording rain gaugeThis definition last updated 08/01/2008