from Wiki :  https://en.wikipedia.org/wiki/Front_and_back_ends

 

In software engineering, the terms front end and back end refer to the separation of concerns between the presentation layer (front end), and the data access layer (back end) of a piece of software, or the physical infrastructure or hardware. In the client–server model, the client is usually considered the front end and the server is usually considered the back end, even when some presentation work is actually done on the server itself.