What is install youtube button on chrome?

I noticed a new button in Chrome on Windows when I have youtube.com opened. This button appears on the address bar.

It asks whether I want to install Youtube app.

What is a youtube app? What is an app in the first place? Does it install a new program on the computer, or is it some kind of add on for chrome? Is this anything useful?

Chrome version: Version 88.0.4324.150 (Official Build) (64-bit)

Solution 1:

It indicates that Youtube can be installed as Progressive Web App:

PWAs are like desktop shortcuts to websites that run in their own separate app window. They don’t take up much space and load faster than navigating to the website in Chrome or Edge. PWAs also get their own icons on the taskbar and won’t add to your swamp of open browser tabs.

The install button appear in Chrome since Chrome 76 if a site meets progressive web app installability criteria:

In Chrome 76 (beta mid-June 2019), we're making it easier for users to install Progressive Web Apps on the desktop by adding an install button to the address bar (omnibox). If a site meets the Progressive Web App installability criteria, Chrome will automatically show an install icon in the address bar. Clicking the button prompts the user to install the PWA.

Youtube can be installed as a Progressive Web App since end of January 2021.