Nuxt.js is a framework for building progressive web applications (PWAs) and universal applications. It is built on top of Vue.js and provides an opinionated structure and set of conventions to streamline the development process. Nuxt.js offers features like server-side rendering (SSR), automatic code splitting for optimized performance, static site generation, and easy configuration. It aims to provide developers with a framework that simplifies the creation of complex applications while maintaining the flexibility and power of Vue.js.