Cylon homeworld
From Battlestar Wiki, the free, open content Battlestar Galactica encyclopedia and episode guide
The planet which the Cylons established as their main base after rebelling against the Twelve Colonies of Kobol, and then fleeing into space to strike out on their own after the first Cylon War.
The Colonials apparently know the location of the planet the Cylons have established as their "homeworld". ("The Hand of God")
The Homeworld allows Cylons who die to be downloaded into another body. However this has a limited range, so the Resurrection Ship allows this for Cylons who die within its proximity. (Resurrection Ship Part I)