CodePen is an online platform that allows users to write and share code snippets in real-time. It primarily focuses on web development, enabling users to experiment with HTML, CSS, and JavaScript. The platform provides a user-friendly interface where developers can see the results of their code instantly, making it a valuable tool for learning and collaboration. Users can create "pens," which are individual projects that showcase their coding skills. CodePen also features a community aspect, allowing users to explore and fork (copy) others' pens, share their work, and receive feedback from fellow developers.