An acronym that refers to the phrase uttered by Britney Spears during a concert in Tampa on March 9th, 2009. Apparently, she had a wardrobe malfunction and didn't realize her mic was still on. After the song ended and the lights dimmed, she exclaimed, "My pussy's hanging out!" Even though, "Oh my god" was not said, omg prefixes the acronym to signal that it is purely netspeak and should not be used outside of the the intrawebz.
by Fiddle Stix December 17, 2009