What is an AU? Is it the singer? (lol sorry for the lame joke) Anyway.

AU or ALTERNATE UNIVERSE.

- means the world is different. The physics, geography, technology etc. are different. Popular in this category are HS (High School) and college fan fictions, where the canon characters are written as students in real world's school. Example, EXO-K members are students in Harvard.

Basically, the character stays the same but the world isn't. SHINee exists but they have supernatural powers, or they're living in Shwadsfgkl street in Asdfkgk town.