Oct
- Microsoft Office 2007
- NASA Institute for Advanced Concepts
- OCT Harbour
- OCT Tower
- OTC (disambiguation)
- Octahedron
- Octal
- Octans
- Octave (electronics)
- October
- Octuple scull
- Odd cycle transversal
- Oklahoma City Thunder
- Olefin conversion technology
- Ontario Certified Teacher
- Ontario College of Teachers
- Optical coherence tomography
- Optimal cutting temperature compound
- Orangi Charitable Trust
- Organic cation transport protein
- Orion correlation theory
- Overseas Chinese Town
- Overseas Chinese Town Limited
- Overseas Chinese Town station
- Overseas countries and territories
- Oxford Classical Texts
- Oxytocin challenge test