>>100009692>>100009707Basically it is the idea that works of fiction, generally that related to comic books but also possibly all of fiction, are all canon and all related in one form or another. I've seen it compared to "the Megatext", which refers to how many works of fiction seem to be similar as if they're based on the same thing (I think all I know about the Megatext I know from one post and it's very short wikipedia page).
Hypercrisis is different because it takes those concepts to an extreme, stating that all these works of fiction actually exist in relation to each other, and also that they can even affect real life. You may have heard of the plane crashing with no survivors is Les Baines? That is often attributed to the Hypercrisis (or meme magic, but depending on how you look at it those could be seen as very similar things). Some interpretations of the theory go so far as to state that works of fiction (not individual characters, but fiction itself) is alive/gaining self-awareness.