| Acronym | Definition |
|---|
| OB | Obstetrics |
| OB | Out (of the) Blue |
| OB | Obligation |
| OB | On Board |
| OB | Oberbürgermeister (German: mayor of a larger city) |
| OB | Observatory |
| OB | Obsolete |
| OB | Obedience |
| OB | Outside Broadcast |
| OB | Oak Bluffs (Massachusetts) |
| OB | Obligatory |
| OB | Oboe |
| OB | Old Boy |
| OB | Oingo Boingo (band) |
| OB | Oskar Blues (brewery; Colorado) |
| OB | Ocean Beach (California) |
| OB | Octave Band |
| OB | Open Box |
| OB | Open Box (gaming clan) |
| OB | Old Babylonian |
| OB | Order of Battle |
| OB | Outboard |
| OB | Oh Baby |
| OB | Occult Blood |
| OB | Out of Bounds (National Park Service or golf slang) |
| OB | Ogre Battle (game) |
| OB | Olfactory Bulb |
| OB | Outward Bound |
| OB | Oil-Based |
| OB | Oberkommando (German: High Command) |
| OB | Official Business |
| OB | Operating Budget |
| OB | Orlando Bloom (actor) |
| OB | Obex (neuroanatomy, part of brain) |
| OB | Opening Balance (financial management) |
| OB | Obliterative Bronchiolitis |
| OB | Ordnance Battalion (US Navy) |
| OB | Out of Business |
| OB | Optical Bench |
| OB | Old Bill (UK police) |
| OB | Open Burning (outdoor fire regulation) |
| OB | Operating Base (US Navy) |
| OB | Organization Behaviour |
| OB | Off Break (cricket) |
| OB | Old Bastard |
| OB | Operational Base (various locations) |
| OB | Overbought (stock market) |
| OB | Operation Battleaxe (gaming) |
| OB | Oversight Board |
| OB | Ohne Befund (German: Results Negative) |
| OB | Outstanding Balance |
| OB | Ordnance Board (US Navy) |
| OB | Oxbridge (summer program) |
| OB | Official Building |
| OB | Odense Boldklub (Danish soccer club) |
| OB | Optical Branch |
| OB | Oberkommandierender (German CINC) |
| OB | Outlet Box (electrical) |
| OB | Office of Budget |
| OB | Over Board |
| OB | Original Budget |
| OB | Open Billing |
| OB | Outdoor Broadcasting |
| OB | Ordinary Break (railway defect) |
| OB | Ohne Binde (German: without a pad; tampon brand) |
| OB | Over Burden (mining) |
| OB | Organization Block |
| OB | Observatoire de Besançon |
| OB | Outbye (mining) |
| OB | Ossewa Brandwag (Ox-Wagon Guard) |
| OB | Ossewa Brandwag |
| OB | Operation Barnabas |
| OB | Onlinebandit (gamesite) |
| OB | Outcast Bandicoot (fanfiction) |
| OB | Old Bedfordian (Bedford School, UK) |
| OB | Ophodni Brod (Croatian: patrol boat) |
| OB | Outer Beings (gaming) |
| OB | Open Along Bit Lines |