Web development involves building, creating, and maintaining websites. It has two broad divisions - front-end development which deals with the user interface using HTML, CSS, and JavaScript, and back-end development which controls behind-the-scenes processes using databases. For example, when a user logs into Facebook, scripts on the back-end receive updates and re-generate the front-end display of the news feed accordingly. Web development is used in industries like mobile apps, entertainment, healthcare, banking, and government organizations.