PWA stands for Progressive Web Application. The main concept of PWA i, it provides all the features of Native App. It provides a feature of Offline user interface.
For example, as we know when we are on localhost with webpack-dev-server and tries to close the reload and again do reload, we can see the application. So here, PWA comes in picture. PWA gives a feature when we are in offline mode, and tries to refresh the page, than also we will be able to see the application working. It uses the concept of Service Worker.
It also provides a feature like Add to Home Screen. For example: I am using Amazon without installed in my device, than if my network is not proper, It will suggest me for Add to Home Screen. At that time, it will create app automatically in your Home Screen.