The Erebus Belt is a planetary debris field located approximately 2 Light Years from the nearest colony, Scorpia. Several thousand years ago a galactic catastrophe formed this belt when a planet was broken apart and splintered into a debris field. It is now a mass of rocks varying in size from small particles to some the size of a Battlestar all trapped in a gravitational flux holding it in its place. Its a good place to hide thanks to the crystalline deposits within the planetoids that confuse DRADIS and as such has been used by smugglers and pirates for centuries. Prior to the attack on the Twelve Colonies the Colonial Fleet always maintained a presence in the region to try to stem such illegal activities as well as get advanced warning of a possible Cylon attack but the truth was it would take an immense number of ships to patrol all of it.
When the initial Cylon attack was underway the Colonial Heavy Liner Alexis used the Erebus Belt to try and hide from the Cylon fleet. Little did they realize that they had a Cylon agent onboard and she opened the air lock to kill the passengers and crew. The Alexis was later discovered by the crew of the Battlestar Hermes who were themselves using the Erebus Belt to hide from the Cylons why they attempted to salvage supplies from Scorpia.