The back-end is the code that runs on the server, receives requests from the client, and contains the logistics to send the right messages back. The back-end also includes the database in which data for the application are continuously stored. The flow of a back-end can be described in three steps: receiving requests, processing requests and sending replies back.
Back-end developers are responsible for managing the exchange of data between the server and the users. Their primary focus lies at the development of all server-side logistics, definition and maintenance of the central database, and ensuring high quality actions and responsiveness on requests from the front-end. They are also responsible for integration of front-end elements in the application. Therefore, basic knowledge of front-end technologies is often necessary too.