Front-end developers are responsible for a website’s user-facing code.
Back end makes the front end of a website possible and stores all the data. The back end of a website consists of a server, an application, and a database. A back-end developer builds and maintains the technology that powers those components which, together, enable the user-facing side of the website to even exist in the first place.
There’s often not a black-and-white distinction between front-end and back-end development. “Front-end developers often need to learn those additional back-end skills, and vice versa, especially in the current economy where marketing is thinly resourced. Developers need some of that cross-discipline. Oftentimes, you have to be a generalist.