Node.js is a platform that enables building real-time web applications using JavaScript. It allows for non-blocking I/O which makes it well-suited for real-time applications like Twitter and Facebook that deliver information to users as soon as it is published. Node.js uses an event-driven, non-blocking I/O model that makes it lightweight and efficient for data-intensive real-time applications compared to other frameworks. Socket.IO is a library that simplifies real-time communication with WebSockets in Node.js applications.