Node.js is an open - source, cross - platform JavaScript runtime environment. It's designed to build fast and scalable network applications. Leveraging an event - driven, non - blocking I/O model, Node.js is highly efficient in handling concurrent operations. It enables developers to use JavaScript on the server - side, which simplifies the development process for full - stack applications. With a rich ecosystem of libraries and modules, it's widely used for web servers, real - time applications like chat and streaming services, and API development.