Used to express great surprise or excitement:ZOMG!! I finally managed to reformat the file...
He broke the Olympic Record with a throw of 90.57 - zomg that's like 57 times my height.
ZOMG okay my love for meat has been rekindled.
There were many a thoughtful gifts: including the (zomg) massage!
Origin
Early 21st century: supposedly resulting from fast or careless typing of OMG, during the course of which the shift key is missed and the 'z' key pressed instead..