From Wikipedia:

The ouroboros or uroboros (/ˌ(j)ʊərəˈbɒrəs/, also UK: /uːˈrɒbərɒs/,[2][3] US: /-oʊs/) is an ancient symbol depicting a serpent or dragon[4] eating its own tail. Originating in ancient Egyptian iconography, the ouroboros entered western tradition via Greek magical tradition and was adopted as a symbol in Gnosticism and Hermeticism and most notably in alchemy. The term derives from Ancient Greek οὐροβόρος,[5] from οὐρά oura ‘tail’ plus -βορός -boros ‘-eating’.[6][7] The ouroboros is often interpreted as a symbol for eternal cyclic renewal or a cycle of life, death, and rebirth. The skin-sloughing process of snakes symbolizes the transmigration of souls, the snake biting its own tail is a fertility symbol in some religions, and the tail of the snake is a phallic symbol, the mouth is a yonic or womb-like symbol.[8]