R. or r. may refer to: * ''Reign'', the period of time during which an Emperor, king, queen, etc., is ruler. * ''Rex (title), Rex'', abbreviated as R., the Latin word meaning King * ''Regina'', abbreviated as R., the Latin word meaning Queen regnant, Queen * or , abbreviated as r., used in historiography to designate the ruling period of a person in dynastic power, to distinguish from his or her lifespan (e.g. "Charles V (r. 1519–1556)") * Abbreviation R., meaning ''"the Crown"'' or ''"State (polity), the state"'' in criminal prosecution in Commonwealth realms (e.g. ''"R. v Defendant"'') * R. (R. Kelly album), R., an album by American singer R. Kelly

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