A static file is a file that is served to the user exactly as it is stored, such as HTML, CSS, and images, in contrast to dynamic files which are processed by the server before being sent to the user, like pages rendered with Django templates or components in a React.js application. In web development, static files are essential for performance and simplicity as they can be cached and served quickly, while dynamic content, created using tools like Django for backend and React.js for frontend, allows for personalized and interactive user experiences. Both static and dynamic content are critical to web development and tools like Django and React.js facilitate the management and creation of dynamic content while also providing mechanisms to serve and manage static files.