A full-stack developer, by definition, is an individual skilled in both frontend development, which pertains to the user interface of the application, and backend development, which relates to the server-side aspects. Essentially, a full-stack developer is capable of managing all facets of development, from the user interface to the server and database, including testing. They possess expertise in HTML, CSS, and JavaScript for the frontend and can utilize languages such as PHP, Ruby, Python, Java, or .Net for the backend. Additionally, full-stack developers should have knowledge of database technologies like MySQL, Oracle, and SQL Server, and may also be responsible for project management, visual design, and web architecture responsibilities.