Node.js is an open-source, cross-platform JavaScript runtime environment that executes JavaScript code outside a web browser. It was created by Ryan Dahl in 2009 and is built on Google Chrome's V8 JavaScript engine. This allows developers to use JavaScript for both client-side and server-side development, enabling full-stack JavaScript applications. Node.js is particularly well-suited for building scalable and high-performance network applications due to its unique features and architecture.