Caching is the process of storing data temporarily to reduce retrieval times and improve performance. By keeping frequently accessed data in a cache, applications can quickly retrieve information without querying the original data source, which can be time-consuming and resource-intensive. Caching can be implemented at various levels, including the browser, server, and database. Common caching mechanisms include in-memory caches like Redis and Memcached, as well as browser caches for web assets. Effective caching strategies can significantly enhance the speed and responsiveness of web applications.