Next.js is a React framework that provides a set of building blocks to create fast and scalable web applications. It is an open-source web development framework created by the private company Vercel. Next.js handles the tooling and configuration needed for React, and provides additional structure, features, and optimizations for your application. It offers server-side rendering and static website generation.
In summary, Next.js is a powerful web development framework that simplifies the process of building fast, interactive applications based on React.