Lightweight Directory Access Protocol (LDAP) is a protocol designed to access directory systems over TCP/IP. Because of this various databases provide an LDAP interface such as Microsoft's Active Directory, Novell's eDirectory, as well as more dedicated LDAP solutions such as OpenLDAP.

Joomla! has had a native LDAP library (joomla.client.ldap (changed to JClientLDAP in Joomla 3.x)) and a native LDAP authentication plugin. This allows Joomla! to authenticate against LDAP systems out of the box: to configure, go to the Plugin Manager and enable and edit the Authentication - LDAP plugin.

You can also read a tutorial on getting started from scratch with LDAP.

Reference: http://docs.joomla.org/Glossary

The mechanism that offers users a stored view of (part of) a web page so that does not have to be pulled from the database. Joomla core offers three levels of caching:

Page caching
View caching
Module caching.

By default, Joomla does not cache any content. When caching is switched on, the stored views for this are stored in the filesystem for Joomla ../cache/page/ folder.