Web development is the creation and maintenance of websites; it's the work that goes behind the scenes to make a website look good, work fast, and run smoothly with a seamless user experience. Web developers, do this using a variety of coding languages.
Web developers design and create websites. They are generally responsible for the look, the site, and the technical aspects, such as the speed of the site and how much traffic the site can handle. Web developers can also create site content that requires technical functionality.