Here's what ChatGPT says about it:

Imagine you have a magical box that you can open on your computer or phone. Inside this box, you can find a mini version of a website that you like to visit. This mini website looks and feels just like the big website, but it works even when you don't have internet! You can play games, read stories, or do other fun things on this mini website, just like you would on the big website. That's a bit like what Apple's Progressive Web App (PWA) is like!