Oh my God! (used to express surprise, alarm, etc.)
Also, omg.
Origin
from its use in digital communications
British Dictionary definitions for OMG
OMG
abbreviation
1.
Oh my God!: used esp in emails, text messages, etc
Word Origin and History for OMG
omg
Internet chat abbreviation of oh my God, by 1994. (Earlier in computerese it meant Object Management Group, 1989, a consortium which helped pave the way for the modern Internet.)