From AMS Glossary
- The amount, usually expressed in millimeters or inches of liquid water depth, of the water substance that has fallen at a given point over a specified period of time.
As this is usually measured in a fixed rain gauge, small amounts of dew, frost, rime, etc., may be included in the total. The more common term rainfall is also used in this total sense to include not only amounts of rain, but also the water equivalents of frozen precipitation. For obvious reasons, precipitation is the preferred general term.