In many Wikipedia pages is written "In-story information". For example, here.
I understand it as "information about the character". Am I right?
It isn't nesisarilay about a character. It is information contained within the story. Information a reader of the story would learn. This excludes meta information such as: Lynda Carter played Wonder Woman in the `70's TV show. Wonder Woman had no idea who was playing her and it wasn't part of the story. Making that part of the story would have been breaking the 4th wall.
Now if we're talking about Deadpool all bets are off.