How it is different from conventional displays ?? I am referring with Chromecast - digital media player developed by Google. The device, a 2.83-inch (72 mm) HDMI dongle, plays audio/video content on a high-definition display by directly streaming it via Wi-Fi from the Internet or a local network.
It usually means that the resolution of the display is higher than something standard, such as standard PAL or NTSC TV resolution. The resolutions most commonly called "HD" are 1280x720 (sometimes "HD Ready" in TVs) and 1920x1080 ("Full HD").
Stores are displaying the latest 4k Ultra high definition TVs now. Some have a curved LCD screen. 8k TVs have been demonstrated by TV manufacturers.
Read all about 4k Ultra High Definition in Google.