Progressive Web App - actually looking at the Camra Site it isn't a PWA. A PWA is a website that you can basically install on a phone - it's coded to use databases in the browser so it can store working data. The Canalplan Tracking app (application stalled at the moment) is a PWA and that stores chunks of maps, locattion details, tracking details and then syncs with the main site when it was a data connection,
So for the CAMRA site if it was a PWA then you could search "Worcester" and it would get all the details and store them on the phone, and if you then re-opened the app it would already have all the data stored.