Update in italics: immediately after posting my comment I see we agree, I just missed it because I had expected a separator between the two formats. I’m going to let my comment be, because it can serve as a reference for others.
4K has to subtypes 4K UHD and DCI which is both 2160 lines, but UHD is 16:9= 3840 pixels wide, and DCI is slightly wider with 4096 pixel in a 256:135 format. But both are “4K”
Wut?
NoUpdate in italics: immediately after posting my comment I see we agree, I just missed it because I had expected a separator between the two formats. I’m going to let my comment be, because it can serve as a reference for others.
1080p = 1920x1080 = “Full HD”
720p = 1280x720 = “HD Ready”, or at least according to wikipedia https://en.wikipedia.org/wiki/Display_resolution_standards “HD”
4K has to subtypes 4K UHD and DCI which is both 2160 lines, but UHD is 16:9= 3840 pixels wide, and DCI is slightly wider with 4096 pixel in a 256:135 format. But both are “4K”
I think you should read your link again. It clearly says 720 is “HD”.
“HD Ready” was a marketing term that was sometimes used for things that were both 720 and close to 720.