Operas 168,211 Officials and employees 91,402 Orchestral music 57,140 Older people 41,478 Organ music 33,545 Officers 24,841 Overtures 23,895 Opera 17,016 Occupations 16,991 Oratorios 16,329 Orthodox Judaism 15,688 Origin 13,879 Organizational change 12,367 Orthography and spelling 12,070 Oceanography 11,527 Obstetrics 11,154 Occupational training 10,171 Occultism 10,149 Orchestre, Musique d' 10,050 Opéras 9,823 Ontology 9,557 Organized crime 9,511 Orphans 9,007 Outdoor recreation 8,904 Organizational behavior 8,517 Orchestral music, Arranged 8,426 Organizational Behavior 8,230 Organization 7,821 Operating systems (Computers) 7,451 Orthodox Eastern Church 7,270 Old age pensions 7,229 Outlines, syllabi, etc 7,078 Organizational effectiveness 6,143 Oncology 5,570 Observations 5,508 Optics 5,485 Oratory 5,457 Ordinances, Municipal 5,392 Organ (Musical instrument) 5,374 Ophthalmology 5,369 Operas, Chinese 5,097 Oral tradition 4,986 Organizations & Institutions 4,958 Orgue, Musique d' 4,903 Oral history 4,855 Online social networks 4,774 Organic compounds 4,620 Olympics 4,390 Operations research 4,361 Obligations (Law) 4,325 Orthopedics 4,322 Obesity 4,061 Ore deposits 4,033 Old age 3,947 Optical data processing 3,947 Oil fields 3,847 Office 3,805 Ouvertures (Orchestre) 3,685 Oil and gas leases 3,649 Oral communication 3,644 Operational readiness 3,515 Ordination sermons 3,496 Office buildings 3,454 Occupational diseases 3,444 Ojibwa Indians 3,405 Orchids 3,295 Organ music, Arranged 3,263 Older women 3,218 Outlaws 3,213 Oaths 3,208 Overland journeys to the Pacific 3,174 Optical properties 3,095 Orphanages 3,054 Oil spills 3,030 Optoelectronic devices 3,004 Ocean 2,938 Old English 2,891 Objectivity 2,813 Optical materials 2,725 Object-oriented programming (Computer science) 2,709 Old age assistance 2,614 Optical instruments 2,610 Opinion publique 2,589 Ordnance 2,531 Opposition (Political science) 2,475 Optical communications 2,466 Organizational sociology 2,400 Otolaryngology 2,391 Organizational Innovation 2,373 Other 2,287 Ocean travel 2,269 Open source software 2,269 Organizational learning 2,261 Ordinateurs 2,204 Oxygen 2,162 Old Norse literature 2,160 Occupied territories 2,136 Organic farming 2,119 Occupational Diseases 2,078 Ornithology 2,060