- OPAC
Use Catalogues - Open area schools
Use Open plan schools - Open government
Use Government policy and/or Right to information - Open learning systems
Use Distance education - Open meadows
Use Open fields - Opera programs
Use Opera programmes - Operas
Use Opera - Operating systems
Use Basic software - Operation Dragoon, 1943-1944
Use Operation Dragoon (1944) - Operation Dynamo, 1940
Use Operation Dynamo (1940) - Operation Sea Lion, 1939-1942
Use Operation Sealion (1940) - Operation Shingle, 1943-1944
Use Operation Shingle (1944) - Operation Smith, 1939-1942
Use Operation Smith (1939-1942) - Operative otolaryngology
Use Otolaryngology - Operative surgery
Use Surgery - Opthalmology
Use Ophthalmology - Optical character recognition
Use Character recognition - Optional courses
Use Elective courses - Orangeries
Use Glasshouses - Orchestra
Use Orchestras - Orchestral works
Use Orchestral music - Orders of knighthood and chivalry
Use Orders - Ordnance
Use Military equipment - Ore deposits
Use Mineral deposits - Organ (musical instrument)
Use Organs (musical instrument)