The Ouroboros, or tail eater, represents the concept of infinity and cycles of succession. It is an old symbol dating back at least to the Hongshan Culture of china, about 5000 to 3000 B.C. Though it has appeared in many different cultures it is from the Greeks we receive the name Ouroboros, which literally means "to devour its tail."
The Ouroboros also makes an appearance in Norse mythology as Jörmungandr, or the Midgard Serpent, a snake so large it encircles the world tree Yggdrasil, and bites its own tail.
In alchemy the Ouroboros represents refinement or purification.