Memcached is a free, open-source, high-performance, distributed memory object caching system that is generic in nature, but designed to speed up dynamic web applications by alleviating the load on the database.
Roughly speaking, the principle is to use an in-memory database that quickly makes the elements stored in RAM available to website users. In more technical terms, it is an in-memory key-value store for small chunks of arbitrary data (strings, objects, etc.) resulting from database calls, API calls or page rendering.
Simple, powerful and designed for quick deployment, Memcached facilitates development and solves many of the problems facing large data caches. Its API is available for most common languages.
