Means: Super Mario Galaxy 2
Super Mario Galaxy is a video game made by Nintendo. And is for the Nintendo Wii. It's the sequel to Super Mario Galaxy. And some Nintendo fans claim it to be the best game in the Super Mario Bros. franchise.
person 1: Do you want to play SMG2?
person 2: Yes! ^___^
person 1: Well too bad. Here... you can play the first one.
person 2: but SMG2 is better than the first one.
person 1: Idc