대박 originally means 1. a very big thing or a very big gourd(a kind of plant looks like pumpkin)/or a bowl made of gourd. But because of internet, we use the expression to describe a very big success. It's kind of slang word but these days everybody knows it.
I think the meaning form the Korean tradition tale of '흥부전', but I am not sure.
헐~ is also a slang word for expressing 'surprising' or absurd things or feelings.
