an oxymoron, used to describe something as being the same as something else. Often used as an excuse for being wrong. Created by Stephanie Graves in the early nineties.
Another way of saying "whatever". It is often confused with "same thing", but you're really saying "OK, I admit that they're not the same thing, but they're not different enough for me to really care about it."
Person A: Hey did you see that raven
Person B: That was a crow
Person A: Same thing
Person B: No it's not
Person A: Fine, Same difference Person B: Watever