A website that behaves like an installed application: it can be added to the home screen, launched without browser chrome, work offline for cached content, and receive push notifications.
A PWA gives much of the app experience without store review, store fees, or a separate codebase. For tools used repeatedly by a known audience it is often enough, and it is the fastest route to a mobile presence.
We add PWA capabilities when there is a real use case — offline access, repeat usage, notifications — rather than by default, and we are explicit that iOS still limits some features compared with a native app.