React is a JavaScript library created by Facebook that enables the creation of user interfaces in a declarative and component-based manner. It has rapidly gained popularity due to its ease of learning, flexibility, and rich ecosystem. React is well-suited for building both simple websites and complex single-page applications (SPAs).
Next.js is a framework built on top of React that offers a range of additional features and conveniences. It enables the creation of universal applications that can be rendered both on the server-side (SSR) and client-side (SPA). Next.js is valued for its SEO optimization, facilitates teamwork, and provides ready-made solutions for common web development problems. This framework is gaining increasing recognition among developers due to its speed, performance, and ease of use.