More specifically, RJ25 is the standard for a three-line phone jack, which seems a little unusual for a hotel room.
Many people (especially outside North America) don't realize that the RJ (Registered Jack) numbers refer to the specific way that the jack is wired, not just the physical size and type of plug.
RJ11, RJ14, and RJ25 are all the same size plugs and jacks, the only difference is whether they are provided with one, two, or three pairs of connections respectively. My guess is that the hotels advertising RJ25 have mistakenly used this number because the jacks are 6-position. They're most likely just a standard RJ11 outlet providing one line.
