Socket.IO is a JavaScript library that enables real-time, bidirectional communication between web clients and servers. It simplifies the process of building applications that require instant data exchange, such as chat applications or live notifications. By using WebSockets and other transport protocols, Socket.IO ensures a reliable connection even in varying network conditions. One of the key features of Socket.IO is its ability to automatically fall back to other methods if WebSockets are not supported by the browser. This makes it versatile and user-friendly, allowing developers to create interactive applications without worrying about compatibility issues.