Full-stack development refers to the development of a website or an application by a full-stack developer. A full-stack web developer is an expert who is well-trained in front-end as well as back-end technologies. The developer who can tackle the server-side, which is one which is behind the scenes, as well as the client-side, which is the one which users interact with, is a full-stack developer.
Front-end developers work with HTML, CSS, and JavaScript. A back-end developer works with Python, PHP, Ruby, etc. A full-stack developer works with HTML, CSS, Python, Ruby, PHP, etc. From development and design to deployment, the entire project is handled by a single person.