Anison is what now?

You know that discussion, if RWBY is anime, right? I think it's not, but... Here's more of the same. I was watching A.I.Channel today and our virtual youtuber is singing songs from "Anison Karaoke Rankings". I guess karaoke boxes compile the numbers of requests? And the No.5 is Supercell's "Kimi no Shiranai Monogatari". I have that track bought at Amazon, DRM-free. But wait, what? What anime was it in again? I even went to Wiki to verify. It's not actually in any anime! Why is it "anison" again? Anison is a genre now?! Wiki has a special classification for it: "J-POP(アニメソング)". Good grief.

UPDATE: A reader informed me that Kimi no Shiranai Monogatari is actually an ED for Bakemonogatari. So all is right with world.