Node.js is a server-side JavaScript runtime built on Chrome's V8 engine, designed for building scalable network applications. It uses an event-driven, non-blocking I/O model that makes it lightweight and efficient, particularly well-suited for data-intensive real-time applications distributed across many concurrent connections. The runtime's single-threaded event loop handles asynchronous operations by offloading work to the system kernel whenever possible, enabling thousands of simultaneous connections without creating thread-per-request overhead. Understanding Node.js means understanding that most operations are asynchronous by default—from file I/O to network requests—which fundamentally shapes how you structure code and handle concurrency compared to traditional synchronous programming models.

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