OSR may refer to: Science and technology Operational sex ratio, of reproductively available males to females On-stack replacement, used by Jikes RVM, a Java virtual machine Optical solar reflector, a radiator material for space craft OEM Service Release, a Windows 95 distribution Open-source robotics Transportation Leoš Janáček Airport Ostrava, in Czech Republic, IATA code OSR Ontario Southland Railway, in Canada Texas State Highway OSR, in the US Other uses Old School Revival, a movement within tabletop role-playing games Owasippe Scout Reservation, a Boy Scout camp in Twin Lake, Michigan, U.S. Orchestre de la Suisse Romande, a Swiss symphony orchestra Operational Situation Reports, or Einsatzgruppen reports, dispatches of the Nazi death squads Ohio State Reformatory, a historic US prison Odessa Soviet Republic, a short-lived Soviet republic Office of Strategic Research, a CIA intelligence analysis organization once headed by Richard Lehman Overseas Service Ribbon, a US military award See also OSR1, a gene OSR2 (gene) BDTH2 or OSR#1, an organosulfur compound used as a chelation agent OSRIC, or Old School Reference and Index Compilation, a Dungeons & Dragons retro-clone