I can say that I use it accidentally without realising(at first) it was a PWA website. So, Im just gonna tell it in layman term.
From what I can tell, its a website, but definitely felt more like an app rather than a website.
the best way to understand it is just to try it. Its just a website(PWA) pinned to your homescreen, so theres not much cost to try it.
PWA apps can run from home screen without address bar, with splashscreen and you can use things like ServiceWorkers (some things can run in background, better caching/storage, you can even run your app offline showing information/data/whatever from last time you synced with backend server).
the best way to understand it is just to try it. Its just a website(PWA) pinned to your homescreen, so theres not much cost to try it.