YouTube's primary site joins YouTube Music and TV as a Progressive Web App (PWA), giving you quick and dedicated access to the site. PWA offers you the streaming site working as its own app of sorts without the address bar and other user interface elements you usually see in the browser. You can pin it to your taskbar or Start menu in Windows, so it's easier to launch YouTube.
You can install YouTube by clicking on the plus-in-a-circle icon at the upper right corner of Chrome's Omnibox. You'll then be prompted to "Install app." As 9to5Google points out, this is different from the browser's manual overflow menu "Install" option, which has been around for a while already.