This document discusses progressive web apps and how Ionic can be used to build them. A progressive web app is a mobile web app that feels like a native app by being installable, having offline capabilities, push notifications, and loading quickly. Building a progressive web app with Ionic allows developers to code once and deploy everywhere while providing a native experience through features like service workers, manifest files, and optimized performance. The document provides links to demo code and examples of progressive web apps built with Ionic.