Node.js is an open - source, cross - platform JavaScript runtime environment built on Chrome's V8 JavaScript engine. It allows developers to run JavaScript code outside of a web browser, mainly on the server - side. One of its core features is asynchronous, non - blocking I/O. This enables Node.js to handle multiple concurrent requests efficiently without getting blocked by I/O operations, making it highly performant under high - traffic situations. Node.js comes with a vast ecosystem of packages through npm (Node Package Manager). Developers can easily find and integrate third - party libraries, speeding up the development process. It's widely used in various scenarios, such as building web servers, real - time applications like chat apps and online games, and command - line tools. Also, it plays a significant role in IoT (Internet of Things) projects, facilitating communication between devices.