Next.js is a production-ready React framework built by Vercel that enables server-side rendering, static site generation, and full-stack capabilities through a file-system-based router. It extends React with powerful features like automatic code splitting, image and font optimization, built-in API routes, and support for both the newer App Router (with React Server Components) and the legacy Pages Router. Understanding that Next.js blurs the line between client and server is crucial—components can run on the server by default in App Router, accessing databases directly, while strategic use of "use client" enables interactivity exactly where needed, creating a hybrid rendering architecture that delivers both performance and developer experience.

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