https://wccftech.com/youtube-just-stopped-classifying-720p-as-high-definition-only-1080p-and-above-is-hd/

For years we've been calling 720p as HD (high-definition). But according to a new change rolled out by YouTube, 720p is no longer HD. Let's fight!

We know how things are in the world of video. If it's 360p or 480p, we straight up call it 'standard definition.' When it's 720p or above, it's 'high-definition.' We further break down the 'high-definition' category into Full HD, UHD and so on. The higher the resolution, the fancier the name gets.