SWR, or Stale-While-Revalidate, is a caching strategy used in web development to improve the performance of data fetching. It allows applications to serve stale data from the cache while simultaneously revalidating it in the background. This means users can see previously loaded data quickly, while the application updates to fetch the latest information. This approach is particularly useful in frameworks like React and libraries such as SWR from Vercel. By using SWR, developers can enhance user experience by reducing loading times and ensuring that data is fresh without interrupting the user interface.