Please note that this article is considered legacy documentation because Fedora 21 has reached its end-of-life support.
Memcached is a distributed, high-performance, in-memory caching system that is primarily used to speed up sites that make heavy use of databases. It can, however, be used to store objects of any kind. Nearly every popular CMS has a plugin or module to take advantage of Memcached, and many programming languages have a Memcached library, including PHP, Perl, Ruby, and Python. Memcached runs in memory and is thus quite speedy since it does not need to write data to disk.