Acronym for Oh, my Voldemort! Only to be used by the faithful servants of the Dark Lord, but ONLY in acronym form, as the mentioning of his name is utterly blasphemous! And if you don't know who the Dark Lord is, then shame on you, and don't ever utter this word!
OMV! Is that the new Death Mask! I've been SO wanting one! All the fashionable Death Eaters are wearing them!