Heinlein used to do the greatest info dumps -- backwards! He'd explain something about us -- the past -- and that would clue us in to how the future is different. It wasn't boring because, hey, it was about us! I remember one book (possibly The Rolling Stones?) in which he describes with horror the internal combustion engine and the cars it powered.
OTOH, a really horrible info dump may be only a sentence or two long. It's that feeling of the author pretending not to talk to the reader while really doing so that's the clue.
"Uh, but he's a Master Wizard, right?"
"Yes."
"So, if he touches me, I turn to dust?"
"That's right. Go, to it boy, and keep out of range!"
is not an info dump.
"Uh, but he's a Master Wizard, right?"
"Yes."
"So, what does that mean, exactly?"
"Well, there are three orders of wizards. The Postulants enter the academy at seventeen. . . . " etc., etc.
is an info dump.