4K Ultra HD Blu-ray movies allow today’s 4K Ultra HD TVs to reach their top picture potential because the content doesn’t have to be compressed to travel over the web. It's the latest generation of Blu-ray discs which, as the name suggests, supports Ultra HD (4K). Besides much sharper pictures, it also adds High Dynamic Range and new advanced audio systems like Dolby Atmos. All this requires higher capacity discs, which is why a new format is required. That means Ultra HD discs won't play on a normal Blu-ray player, though you can play older Blu-ray discs on an Ultra HD player.