Displays differ from one another mainly based on the measurement of pixels it supports. Regardless of the screen size, if the pixel stays at this measurement it will be the same display.
HD High Definition is the most familiar format since it has become the standard for the television viewing experience in households around the world. Any video image with a resolution of 1280*720 pixels a 16:9 aspect ration is defined as HD.
Full HD this one is the higher step of HD, and its defined by the support of 1920*1280 pixels.
Most consumers have upgraded their TVs and monitors to 720p/1080p to see crisper, more life like images.
Quad HD or 2K (QHD) offers a more detailed view, having four times the vertical resolution of standard 720p HD to 2560*1440 pixels.
Ultra High Definition (UHD) This format delivers what is considered to be the best viewing experience. 4K refers to a horizontal resolution of approximately 4,000 pixels. 4K displays have a resolution of 3840*2160 in an aspect ratio of 16:9 which is four times the Full HD resolution of 1080p