https://www.cnbc.com/2017/09/12/apple-tv-4k-unveiled.html

Apple just revealed its new Apple TV 4K, a set-top box that supports sharper resolution TV shows and movies.

4K video content is becoming more common and has already been offered in products from competitors including Amazon, Google and Roku. It offers 4x more pixels than HD, which means you're getting a much sharper video quality. It also supports HDR content (short for high dynamic range) which offers more details and color. Apple TV 4K supports HDR10 and Dolby Vision, two HDR standards.