A Full Stack Developer is a professional who can handle all layers of software development, including front-end and back-end tasks. They are skilled in programming languages used for front-end development like HTML, CSS, and JavaScript, and also back-end languages like Python, Ruby, or Java. They manage databases, servers, and systems engineering. They design user interactions on websites, develop servers and databases for website functionality, and code for mobile platforms. They are capable of creating a complete, functional web application single-handedly, from designing the user interface to implementing the server-side logic. They also troubleshoot, debug, and improve usability.