Operas 168,228 Officials and employees 91,425 Orchestral music 57,158 Older people 41,486 Organ music 33,550 Officers 24,842 Overtures 23,898 Opera 17,024 Occupations 16,997 Oratorios 16,330 Orthodox Judaism 15,689 Origin 13,884 Organizational change 12,376 Orthography and spelling 12,073 Oceanography 11,528 Obstetrics 11,155 Occupational training 10,171 Occultism 10,153 Orchestre, Musique d' 10,076 Opéras 9,844 Ontology 9,559 Organized crime 9,514 Orphans 9,009 Outdoor recreation 8,906 Organizational behavior 8,521 Orchestral music, Arranged 8,428 Organizational Behavior 8,225 Organization 7,822 Operating systems (Computers) 7,451 Orthodox Eastern Church 7,270 Old age pensions 7,230 Outlines, syllabi, etc 7,078 Organizational effectiveness 6,145 Oncology 5,572 Observations 5,508 Optics 5,483 Oratory 5,457 Ordinances, Municipal 5,392 Organ (Musical instrument) 5,374 Ophthalmology 5,370 Operas, Chinese 5,113 Oral tradition 4,989 Organizations & Institutions 4,959 Orgue, Musique d' 4,910 Oral history 4,857 Online social networks 4,782 Organic compounds 4,620 Olympics 4,391 Operations research 4,362 Obligations (Law) 4,328 Orthopedics 4,324 Obesity 4,062 Ore deposits 4,037 Old age 3,947 Optical data processing 3,946 Oil fields 3,848 Office 3,805 Ouvertures (Orchestre) 3,690 Oil and gas leases 3,649 Oral communication 3,644 Operational readiness 3,516 Ordination sermons 3,496 Office buildings 3,454 Occupational diseases 3,445 Ojibwa Indians 3,407 Orchids 3,295 Organ music, Arranged 3,263 Older women 3,218 Outlaws 3,214 Oaths 3,210 Overland journeys to the Pacific 3,174 Optical properties 3,095 Orphanages 3,055 Oil spills 3,030 Optoelectronic devices 3,003 Ocean 2,941 Old English 2,893 Objectivity 2,813 Optical materials 2,729 Object-oriented programming (Computer science) 2,710 Opinion publique 2,620 Old age assistance 2,614 Optical instruments 2,611 Ordnance 2,534 Opposition (Political science) 2,475 Optical communications 2,466 Organizational sociology 2,400 Otolaryngology 2,391 Organizational Innovation 2,374 Other 2,288 Ocean travel 2,271 Open source software 2,270 Organizational learning 2,261 Ordinateurs 2,203 Oxygen 2,162 Old Norse literature 2,160 Occupied territories 2,137 Organic farming 2,119 Occupational Diseases 2,079 Ornithology 2,061