The Ouroboros symbolizes the cycle of life (life, death and rebirth) and the infinity and immortality of it.
This ancient symbol is used by many peoples; for example the ancient Greeks (Plato described the Ouroboros as the first living mythological beast of the Universe), the Middle East, India, China, Japan, Aztecs, Native Americans, the ancient Norwegian mythology and many more. In 2001 and 2009 the Ouroboros was also seen in crop circles.
The torus is a shape that is commonly found in nature, often in the form of energy. It is recently discovered that our hearts have an electromagnetic field, shaped like a torus. Just like the magnetic field of the Earth. But also wormholes, black holes and white holes are shaped like a torus. But also matter can take the form of a torus, for example an apple or the fetus (for a short period of time, the mouth and anus of the fetus form a torus).