4K resolution
4K resolution, also called 4K, refers to a horizontal display resolution of approximately 4,000 pixels. Digital television and digital cinematography commonly use several different 4K resolutions. In television and consumer media, 38402160 (4K UHD) is the dominant 4K standard, whereas the movie projection industry uses 40962160 (DCI 4K).
Apple TV
The 1st and 2nd generation Apple TV video output can be set to either 1080i or 1080p; however, this resolution is limited to the user interface and the viewing of photographs – all other content is simply upscaled to those resolutions. Those models cannot play 1080i or 1080p video content (e.g., HD camera video). The 3rd and 4th generation Apple TV support 1080p video content. The Apple TV 4K, as the name suggests, supports 4K resolutions and HDR, including Dolby Vision. 4K content from sources such as iTunes can be played on a compatible 4K television set.