Progressive Web Apps are handled by the browser. The main difference wrt. "web apps" is that they're not presented to the user with a "web-site" UX. See https:

Progressive Web Apps are handled by the browser. The main difference wrt. "web apps" is that they're not presented to the user with a "web-site" UX. See https://xkcd.com/1367/ https://xkcd.com/1367/ for a summary of why that's a good thing.