The resolutions you see in the video specification — 720p, 2K, 4K—represent the number of horizontal lines a video has from top to bottom. So, a 720P video is made up of 720 lines stacked one on top of another, with each line being 1080P pixels wide. In other words, a 720P video has a resolution of 1280p ×720p pixels.
For comparison, a 480p HD video has 480 lines that are each 852 pixels wide, meaning that it is more than twice as sharp as the same video at 360p and can be viewed on a much larger screen.
Videos at 144p are the lowest resolution for the video to smartphones and other mobile devices since they use up the lowest data but appear total blur screens.
Video at 244p is better than 144p but still not so good, it appears less blurry than 144p but still not so clear on the smartphone screen
360p video has a decent resolution for low range and small screen smartphone but it appears blurry on a big screen
480p videos resolution are more clear then 360p but it still may appears blurry on big screen but it appears decent on smartphone
720p videos are also called HD video and appears very good on smartphones and big screen but the detailing is not that great
1080p videos are also known as full HD and appear very good one smartphone screen and as well as the big TV screen
2K resolution is also known as 2560×1440, 2k is officially considered Quad High Definition (QHD)
4k means 4 thousand horizontal lines, 4K is equal to 3840 x 2160 pixel (4K UHDTV) resolution, 4k is one of the best resolution for human view
The 8K video 8000 lines horizontally Or 7680 x 4320 pixels, 8K resolution is 16 times better than the 4K video