This document discusses progressive web apps (PWAs), including what defines their usage, how they work, and their key characteristics. PWAs are defined as progressive, responsive, connectivity independent, app-like, fresh, safe, discoverable, re-engageable, installable, and linkable. Service workers play an important role in PWAs by running in the background, enabling features like caching and push notifications. For a user to add a PWA to their home screen requires an web app manifest, service worker, HTTPS connection, and visiting the web app twice within 5 minutes.