A PWA is a website that behaves like a mobile app: it can be installed on the phone's home screen, works offline and sends notifications – without going through the App Store or Google Play.
PWAs use modern browser capabilities to blur the line between site and app: a home-screen icon, full-screen operation, caching that allows offline work.
For many companies a PWA is the golden mean: costs close to a website (one codebase instead of separate iOS/Android apps) with an app-like experience. It excels in product catalogues, internal tools and services where the barrier is users' reluctance to install yet another app.
Limitations: PWAs have weaker access to system features (especially on iOS) and less presence in app stores. We advise honestly: sometimes a PWA is enough, sometimes you need the full app.