The root object identifier from which MIBs produced by other companies may be placed. MIBs produced by other enterprises are typically implemented with the object identifiers as defined in the MIB, but if the MIB is deemed to be uncontrolelled, we may reroot the MIB at this subtree in order to have a controlled version.
Sources for this description
Multiple manufacturers; see the original MIB MIB copies (LibreNMS/Observium Community)