An app represents your application where users logs in.
An app is typically a web server but today SPA and native apps are also common.
|Mobile, Desktop, Smart device and CLI (e.g., Android, Apple TV, iOS.)
|Single Page Application (SPA)
|Typically a web server (e.g., Node.js, Golang, PHP)
|Machine to Machine
|Server side worker such as daemon or a micro service.