It is the part of the application the user interacts with.
Unless the application is standalone, it is a pure user interface,
a view on the data.
No business logic is coded here, the business logic being in the Back-End
Depending the targeted usage of the application (desktop or mobile or both), the appropriate technologies must be chosen:
- Single Page Application (SPA) or server side rendering,
- native mobile app or SPA or web responsive.