It stands for: Room Temperature Vulcanizing (elastomer sealant)
elastomer = Any of various polymers having the elastic properties of natural rubber.
Vulcanizing = To improve the strength, resiliency, and freedom from stickiness and odor of (rubber, for example) by combining with sulfur or other additives in the presence of heat and pressure.
In other words, the stuff sets up (cures) into a rubber like material at room temp.
A good site is:
www.dictionary.com Just found it myself.