Doesn't mean for a couple, and shouldn't mean just a double bed. It means a room at least three times the area of a double bed. I think that's a good definition. However you'll find a lot of people defining it has having a double bed in it, meaning the rest of the room is as roomy as a charter flight to Malaga in August.
By the way its also kind of worth enquiring about the quality of the bed, or finding out for yourself by sitting on it.
'O' is for orthopaedic, 'B' is for bouncy castle.