Node.js is an open-source, cross-platform JavaScript runtime environment that allows developers to execute JavaScript code outside the web browser. Built on the powerful V8 engine from Google Chrome, Node.js is designed for building fast, scalable, and efficient server-side and networking applications. Its non-blocking, event-driven architecture makes it ideal for real-time applications such as chat systems, online gaming, streaming services, and APIs. Node.js uses a single-threaded event loop to handle multiple requests simultaneously, which helps in managing high-concurrency tasks without slowing down performance. With access to the vast npm ecosystem, developers can leverage thousands of pre-built packages to speed up development. Node.js supports modular development, integrates well with databases like MongoDB, and is widely used in full-stack JavaScript development alongside frontend technologies. Popular frameworks like Express.js simplify building RESTful APIs. Its performance, scalability, and wide adoption by companies like Netflix, PayPal, and LinkedIn make Node.js a preferred choice for modern backend development.