OEM - An acronym, "Original Equipment from Manufacturer," refers to parts or components.
O.F.F.O. (OFFO) - Outlaws Forever Forever Outlaws
Odometer - Device that stores the mileage (distance driven). Usually located on the speedometer.
Old Lady - Wife or steady girlfriend of a club member.
Oil Bag - Oil tank
Oil Dripper - Slang term, refers to the earlier American and British bikes and often still used towards the modern ones.
Oil Pressure Warning Light - Too Late Light
On Rails - Expression when a motorcycle holds a corner extremely well at speed. (The bike felt like it was on rails through that corner).
One Percenter (1%er) - Worn by outlaw clubs. Made famous by the media that said 99% of bikers and clubs are law bidding citizens the other 1% is not.
One-Off - One-of-a-kind fabricated part
One-way SOB - Selfish, takes but does not give in return
OPG - Oil Pump Drive Gear (used normally to refer to the infamous plastic oil gears in Kawasaki Vulcans)
Organ Donor - A biker who doesn't wear a helmet
Originals - A member's first set of colors which are never to be cleaned.
Oscar - Blue haired Buick driver. "Oscar almost turned left in front of me"
OTB - Over The Bars as in a crash