What is a progressive web app?

Two pieces do most of the work. A manifest file tells the browser the app's name, icon and how it should launch, which is what allows an installed, chrome-free window. A service worker sits between the page and the network, caching responses so the app opens instantly and keeps working when the connection drops. Everything else is an ordinary website.

Support is uneven in ways that matter commercially. Installation on iOS is a manual, undiscoverable gesture rather than a prompt, and several capabilities available on Android are restricted or absent. You also give up store presence entirely, so if a meaningful share of your users expect to find you by searching the App Store, a PWA solves the engineering problem and not the distribution one.