Node.js is an open-source, cross-platform JavaScript runtime environment that executes JavaScript code outside a web browser. Built on Chrome's V8 JavaScript engine, Node.js allows developers to use JavaScript for server-side scripting, enabling the creation of dynamic web content before the page is sent to the user's browser. Node.js is known for its non-blocking, event-driven architecture, which makes it ideal for building scalable and high-performance applications, such as real-time web services, APIs, and microservices. Its package ecosystem, npm (Node Package Manager), provides a vast repository of modules and libraries that extend Node.js functionality and streamline development.