In the context of the
Microsoft Windows NT line of
computer operating systems, the
relative identifier (RID) is a variable length number that is assigned to objects at creation and becomes part of the object's
Security Identifier (SID) that uniquely identifies an account or group within a domain. The Relative ID Master allocates security RIDs to DCs to assign to new AD security principals (users, groups or computer objects). It also manages objects moving between domains.