Korean slang means "Awsome, Unbelievable" These days, lots of Korean say this when they watched, heard or tasted something nice, unbelievable, great. It is... "대박(Dae-bak)" Its original meaning is good luck. It was used like this: for an example, when your friend have an important job interview or test, you could say "대박 나라!(Dae-bak nara, I wish you would pass the exam or Good luck)" Currently, its usage has been getting wide. People use this word when they express their suprising. I can say it is very similar to OMG Try to use this word in conversation. You will look like very Korean. But, please keep in mind it is not the appropriate word for your boss, a teacher and your business partner.