This is a normal web application that gives a feel of a native application to the user. It uses a modern browser. This is capable of working offline, for example, Pinterest is a PWA so we can install it as an application, we will get it as an independent application and it will work offline.
The web application must be served over a secure network. It uses a service worker as a script that works in the background. Like a native application, it receives notifications, and also there are automatic self-updates.
It can fit any desktop, tablet, mobile, and any other technology. It served using HTTPS to ensure that the apps and their content are always secure.