I'd call it an electronic music festival (or a giant rave, because terms like "EDM festival" were invented by corporations to displace "rave" the same way "open source" was meant to sanitize "free software" and Fusion is not a corporate event). I wouldn't call it a psytrance festival - that's just what they play on one stage of many, and maybe the 3rd or 4th biggest. There's a stage run by people from Berghain that plays techno the whole time (my favorite), a drum-n-bass stage, a couple more electronic music stages that I'm not sure about the subgenre, some smaller stages where live rock and metal bands play, theater performances, some kind of car racing thing next to a circus-looking tent, neither of which I've visited. And what the heck is "the hotel"?
I only know Fusion festival from the psytrance community so I didn't realize it was a multi genre festival, but that makes sense!