OMG is a short way of writing Oh my God. People type it when they are surprised, shocked, or very pleased — in messages, comments, and emails. Young people also say the three letters out loud: 'O-M-G'. It is very informal. You would not put it in a school essay or a letter to a teacher. Though actually, some people feel 'God' in the longer phrase is too strong, so they write 'oh my gosh' instead, or just OMG to soften it. The first time it showed up in print, it was also a little joke on a British honour called the Order of St Michael and St George, whose letters are the same; that joke is forgotten now. Today it is simply chat English for 'I cannot believe this.'