An auto-regeneration unit is a Borg device. It is spherical in shape and can crawl around on its own autonomously even after its ship is destroyed.

An object suspected to be a functional auto-regeneration unit was amongst the technology salvaged from the debris of a Borg probe destroyed by the USS Voyager in 2375. Captain Janeway initially mistook it for a transwarp coil. (VOY: "Dark Frontier")