@emotion/server provides server-side rendering (SSR) utilities for Emotion, a popular CSS-in-JS library. It allows you to extract CSS generated during server-side rendering to avoid flash of unstyled content (FOUC). This package is crucial for improving user experience and SEO when using Emotion in applications that render content on the server, ensuring consistent styling between the server and client environments. It includes methods for collecting styles and injecting them into the HTML markup.