A i Y o gyngor
- Occasional work See Part-time work
- Occupational pensions
- Occupational sickness See Industrial injuries
- Official Receiver
- Old age pensioners See Older people
- Old people See Older people
- Old people's homes See Care homes
- Older people
- Ombudsman
- Ombudsman Services: Property
- Order for sale
- Order to obtain information
- Organ donation
- Organisations
- Outpatients See National Health Service
- Overseas See Abroad
- Overseas students See Students
- Owner occupiers
- Owning property jointly See Joint ownership