Operas 168,258 Officials and employees 91,443 Orchestral music 57,186 Older people 41,510 Organ music 33,554 Officers 24,842 Overtures 23,904 Opera 17,023 Occupations 17,000 Oratorios 16,331 Orthodox Judaism 15,693 Origin 13,878 Organizational change 12,385 Orthography and spelling 12,072 Oceanography 11,535 Obstetrics 11,156 Occupational training 10,174 Occultism 10,153 Orchestre, Musique d' 10,114 Opéras 9,891 Ontology 9,563 Organized crime 9,522 Orphans 9,014 Outdoor recreation 8,909 Organizational behavior 8,532 Orchestral music, Arranged 8,434 Organizational Behavior 8,226 Organization 7,823 Operating systems (Computers) 7,454 Orthodox Eastern Church 7,271 Old age pensions 7,237 Outlines, syllabi, etc 7,077 Organizational effectiveness 6,146 Oncology 5,574 Observations 5,510 Optics 5,486 Oratory 5,457 Ordinances, Municipal 5,392 Organ (Musical instrument) 5,373 Ophthalmology 5,372 Operas, Chinese 5,112 Oral tradition 4,988 Organizations & Institutions 4,959 Orgue, Musique d' 4,917 Oral history 4,860 Online social networks 4,786 Organic compounds 4,621 Olympics 4,392 Operations research 4,367 Obligations (Law) 4,333 Orthopedics 4,326 Obesity 4,064 Ore deposits 4,039 Old age 3,950 Optical data processing 3,947 Oil fields 3,849 Office 3,787 Ouvertures (Orchestre) 3,703 Oil and gas leases 3,651 Oral communication 3,644 Operational readiness 3,516 Office buildings 3,456 Ordination sermons 3,455 Occupational diseases 3,447 Ojibwa Indians 3,407 Orchids 3,295 Organ music, Arranged 3,264 Older women 3,219 Outlaws 3,215 Oaths 3,211 Overland journeys to the Pacific 3,167 Optical properties 3,094 Orphanages 3,055 Oil spills 3,029 Optoelectronic devices 3,005 Ocean 2,944 Old English 2,892 Objectivity 2,812 Optical materials 2,733 Object-oriented programming (Computer science) 2,710 Opinion publique 2,625 Old age assistance 2,614 Optical instruments 2,612 Ordnance 2,533 Opposition (Political science) 2,476 Optical communications 2,467 Organizational sociology 2,404 Otolaryngology 2,393 Organizational Innovation 2,374 Other 2,289 Ocean travel 2,272 Open source software 2,270 Organizational learning 2,264 Ordinateurs 2,201 Oxygen 2,163 Old Norse literature 2,162 Occupied territories 2,138 Organic farming 2,120 Occupational Diseases 2,078 Ornithology 2,061