Next.js is an open source web framework built on React and maintained by Vercel, which adds what React needs to ship a complete site or application: routing, server-side rendering, static page generation and performance optimization.
In practice, each file in a folder becomes a page. The developer chooses page by page whether content is generated ahead of time, on each request or in the browser. Since version 13 and its App Router, Next.js is organized around React Server Components, which run part of the interface on the server.
It is one of the most common choices for starting a React project, from marketing sites to SaaS applications. It can be deployed on Vercel or on any hosting able to run Node.js.
Why it matters when hiring
Next.js is quick to learn on the surface, much less so in depth. A strong profile can explain when to render a page on the server or the client, how caching works, and what the App Router changes compared to the old model. The trap: a developer who has only used templates and cannot diagnose a slow page.