I'm not saying the word is a fandom invention. The ruling and application of it is what's bizarre. The way people will blindly invalidate everything except the manga for reasons they sometimes haven't even questioned. In threads like this, I get why. But for entertainment value, it's nonsense you only find in media with cult followings.
But even in other cult followings, ones that might need an existing canon (Harry Potter slashfics or Star War's reset canon) they're not usually taken that seriously or religiously, they're essentially a viewing guide.
Narutobase and anime has a fandom that has has no such reason other than 'I dont like it so it didn't happen'. Which is basically denial, seeing people bicker over exactly how many of the novels are canon, or which movie had Godkishi's approval is so pointless when it's all there to entertain. Never been just one person behind the series.
Sorry to go off on one, just trying to be clearer.