Yes, it's "waitlist". That means the the entire category is currently sold out, but they will still sell that category even though it's full in hopes of an opening becoming available. Personally, I wouldn't book it.
For our Christmas cruise that was sold out for months ahead of time, they were still accepting waitlists for our Category GS up until the day of sailing. There are only 2 of these cabins. IMO, this is a stupid move on Princess' part when the final payments have been paid, documents sent out and passengers obviously cruising in those cabins and there's no availability. It means possibly having to disappoint someone in the end. In a mini-suite category, you might have more of a chance, but still, it's risky, IMO.