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

In Joomla! an Article is a piece of content consisting of text (HTML), possibly with links to other resources (for example, images). Articles are the basic units of information in the content system and the bottom level in the content hierarchy. Since Joomla! 2.5 , each Article is in exactly one Category. A Category can be in another Category making it a sub Category. It is also possible to have Uncategorised Articles. These articles exist without being associated with any Category.

Before Joomla! 2.5 and earlier versions, an Article was the third level in the hierarchy Sections ? Categories ? Articles. Now an Article is a bottom level and will alway be the second level or greater in hierarchy.

Category ? Articles
Category ? sub Category ? Articles
Category ? sub Category ? sub Category ? Articles

Articles are maintained using the Article Manager (see the Content Article Manager for or the Content Article Manager for ) which can be reached in the Administrator (Back-end) by clicking on the Content menu, then the Article Manager menu item.

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

Files that gives you control over the display of modules or components.

Override files are placed in special folders and can be used in place of the standard layout files. Unlike Template Overrides, which override layout files of the same name, Layout Overrides are additional layout files that give you more options and control.

Application programming interface. The published methods for using a set of programs. In Joomla, the API refers to the public methods and fields of all the defined classes, especially ones in the Joomla platform. Because third-party programs rely on the API, it should be changed as infrequently as possible and always with advanced notice.