From AMS Glossary
Popular term applied to all activities designed to increase, through any artificial means, the amount of precipitation released from a cloud.
The techniques of cloud seeding have been studied carefully and extensively, especially since V. J. Schaefer's discovery of the effect of dry ice on supercooled clouds.
Schaefer, V. J. 1946. The production of ice crystals in a cloud of supercooled water droplets. Science. 104. N.Y., . p. 457.