Memcached is an open source, high-performance distributed memory object caching system that acts as an in-memory key-value store for arbitrary data. It's commonly used to speed up dynamic web applications by caching the result of expensive queries made to a relational database, providing a significant boost in response time. Memcached stores data in memory, making writing and reading from the store extremely fast compared to disk-based operations, but the data is volatile and should not be used as a permanent data store. The Datadog Agent can collect key metrics from Memcached, including system memory, fill percent, evictions, hits, and misses, which are essential for monitoring the general health and usage of the cache. By installing the Datadog Memcached integration, developers can monitor these metrics and ensure that their cache is functioning correctly, helping to speed up their web applications.