The ourobouros (also spelled ouroboros, uroboros, aroboros), is a usually circular symbol of a creature (traditionally a serpent, lizard or dragon) following, biting or consuming it's tail in an endless loop. Many modern interpretations have also become popular now, such as impressionistic works like 'Drawing Hands' by Escher.
Though frequently thought of as a medieval symbol, images of such a thing have been seen as early as 1600 BC in Egypt, Japan in the 14th century and Meso-America in the 1500's. The name we know it as, however, comes from the Greek for "tail eater" (ouro = tail or remainder, boro = to consume, as english bore).
Though an undoubtedly popular symbol throughout history, the meaning has never remained concrete and has been reshapped by whoever adopted the symbol. It has been a representation of people and Deity through the ages, from Isis and later Abraxas in ancient Egypt to Jormungand, the serpent of Midgard, in Norse legend. It also serves to represent many philosophies and ideas, from the cyclical nature of reality, the karmic cycle and chaotic interplay to even such things as thermodynamics and the nature of matter and energy.
Red Dwarf Note: as ohe marks, Dave Lister's box was inscribed with the name ourobouros. But when he was told later in life about it, he understood it as "our Rob or Ross" and thought that it meant that his biological parent's couldn't decided on naming him "Rob" or "Ross".