We've learned now that the water vapor that makes up clouds can come from evaporation which means liquid water molecules floating away into the air.
Sometimes it's really cold out, and the liquid water turns solid and becomes snow and ice.
Remember that things like water can be three different types: Solid - ice, Liquid - water, Gas - steam/vapor
When the water is solid ice or snow, the excited water molecules are still going to shoot off into the air and become water vapor.
But because the water vapor came from a solid like ice instead of a liquid like water, it is called submlimation.
To put it a little simpler:
When water vapor is made from liquid water it is called evaporation.
When water vapor is made from solid water it is called sublimation.
(from: wikipedia - snow)
Kid Facts - Blast from the past: Tephra
