The only pool-related activities one could engage in on a cruise ship would involve swimming, as any attempts at snooker or billiards would be quickly undone by the motion of the ocean. To the rescue are these special pool tables, fitted with gyroscopes to keep them level, regardless of what the waves are doing.
The clip above was taken back in 2011 on the cruise ship "Radiance of the Seas", however, they're apparently available on all of Royal Caribbean's Radiance-class ships. That said, the Radiance was the first to get them.
The video above is the one currently doing the rounds, but if you want a better look at how the table moves, the time-accelerated clip below is what you want.