What exactly does a back-end development programmer do?

What exactly does a back-end development programmer do? In reality, even though the front-end development has won most of the glory, most of the code (arguably the most useful code) that exists in the world is the back-end code that the end user will never see. The front-end developer builds the user interface, and the back-end developer writes the code to make it work; Back-end developers write code that makes buttons work by pointing out what data is extracted from the database and sending it back to the front end. What does a back-end development programmer do? Let's be specific.