They mean that they're not going to limit the total amount of data that you send/receive beyond the natural limit implied by the maximum rate.

When a movie subscription says unlimited movies, we know they're not suggesting that they can break the laws of time, just that they won't turn you away from a screening. It's pretty normal language, used to communicate no additional limit, which is relevant when compared to cell phone data plans (which are actually, in my opinion, fraudulent) that shunt you to a lower tier after a certain amount of usage.