The impartial third party within an Engineering outfit that holds onto the “released” documentation so that the originating group has no opportunity to violate any of the four rules by re-writing history to hide any errors. The concept of an ERU is intrinsic to demonstrating process integrity, rather than just claiming it.
An ERU also serves as a long-term repository for the documentation. It is typically identified by way of a CAGE code; any given ERU might be able to release documentation against more than one code, but release authority for any given code typically resides with only one ERU at any point in time.