From AMS Glossary
A type (or form) of precipitation consisting of water droplets less than 0.5 mm (0.02 in.) in diameter and larger than 100 nm.
Droplets larger than 0.5 mm are considered raindrops. Drizzle usually falls from low stratus clouds and is frequently accompanied by low visibility and fog. In weather observations, drizzle is classified as 1) light, the rate of fall being from a trace to 0.3 mm (0.01 in.) h−1; 2) moderate, the rate of fall being from 0.3 to 0.5 mm (0.01–0.02 in.) h−1; and 3) heavy, the rate of fall being greater than 0.5 mm (0.02 in.) h−1.
Term edited 1 November 2016.