The largest a ship can be while still able to go through the locks of the Panama Canal.
Royal Carribeans Radiance Class of Ships is Panamax, you can't go on a panama canal cruise on a bigger ship.
Ships classified as Panamax are of the maximum dimensions that will fit through the locks of the Panama Canal, each of which is 1000 ft long by 110 ft wide and 85 ft deep. Thus a Panamax ship will usually have dimension of close to 965 ft long (294m), 106 ft wide (32.3m) and a draft of 39.5 ft (12.04m). This is a tight fit that leaves little margin for piloting error.
Royal Carribeans Radiance Class is the way to go for panama canal cruises. It's the largest cruise ship that can go through the Panama Canal.