In web development, front-end (or client-side) is the text, mark-up, and code that ends up in the user's web browser and is therefore processed by the browser. This typically includes HTML text mark-up, CSS styling, and JavaScript code. Back-end (or server-side) is the code that runs on the web server, which can be in any of many different programming languages, and typically interacts with a database of some sort. It ultimately generates everything that gets sent to the browser (where the front-end takes over and processes it).