OM3 Share definition Flag An adaptation of OMG (oh my god) used when talking about threesomes. Some people got all riled up over an upcoming episode of Gossip Girl in which three of the show's characters engage in an OM3. OM3 by dwigtdwigt November 4, 2009 0 0 Get merch Get the OM3 mug. Buy Now — $32.95 See more merch
