Abbreviation Meaning
Ob, Obby A Summoning obelisk, a Soul Obelisk in Menaphos, the Wilderness Obelisk
Occ An Occult floor in Daemonheim.
Off, Get off Stop attacking
Omni Omnipower ability
One-iteming Using a single item (usually weapon) to minimise risk when player-killing
Ons, Onsl Onslaught
Ooo Orb of oculus
Ovl(s) Overload potion. Can also be used as a verb indicating to take a sip of an Overload potion.
ob x m  Overload boxing x mil
OP Over-powered