Node.js is an open-source, cross-platform runtime environment that allows developers to run JavaScript code on the server side. Built on Chrome's V8 JavaScript engine, Node.js is known for its non-blocking, event-driven architecture, which makes it highly efficient and suitable for building scalable, real-time applications, such as chat applications, online gaming, and streaming services. Node.js enables developers to use JavaScript for both front-end and back-end development, creating a unified development environment and reducing the need to learn multiple languages for different parts of an application.

One of Node.js's key strengths is its ability to handle a large number of simultaneous connections with minimal overhead, thanks to its event-driven, non-blocking I/O model. This makes it particularly well-suited for applications that require high concurrency, such as web servers, API services, and microservices architectures. Node.js also boasts a vast ecosystem of packages and modules available through the Node Package Manager (NPM), which simplifies the development process by providing reusable components for a wide range of tasks. Despite its strengths, Node.js may not be the best choice for CPU-intensive tasks due to its single-threaded nature, but its versatility, efficiency, and strong community support have made it a popular choice for modern web and mobile application development.