- O-Ring
- Obsolescence
- Online Real Estate Listings
- Open House
- Open Listing
- Open Mortgage
- Open Space
- Option
- Option Listing
- Oral Agreement
- Orange Peel
- Oriented-strand Board
- Original Principal Balance
- Origination Fee
- Ostensible Agency
- Out
- Outbuilding
- Overflow Plate
- Overflow Prevention Switch
- Overhang
- Overimproved Property
- Owner Financing