Next.js is a framework for building server-rendered React applications. It is built on top of Node.js and provides a set of features that make it easy to build performant, scalable applications. One of its key features is automatic code splitting, which ensures that only the code needed for a specific page is loaded, resulting in faster load times.

Next.js also has a built-in development server with hot-reloading, making it easy to develop and test your application. It also have automatic static optimization, it means it automatically generates a static version of your application when you build it for production.

Another feature is Server-side rendering of React components, which can improve the performance of your application by reducing the amount of work that needs to be done on the client-side. Next.js also has a built-in routing system that makes it easy to create dynamic pages and handle different types of requests.

It is a versatile and powerful framework that is well suited for building high-performance web applications, both simple and complex.