Programming technique based on using classes, objects, and methods - an approach to designing modular reusable software systems. Joomla is based on OOP. Solid understanding on OOP is a key plus when working with Joomla programs.

The database managment system used by most Joomla installations and by most dynamic websites in the world.

A user level on a Joomla site that by default can access only the front end. Editors have privileges to post and edit content, but no permission for publishing content.

The database table prefix is a string (a few characters long) prepended to the name of Joomla!'s tables. Using a prefix enables you to run multiple installations of Joomla! using a single database.

The database table prefix can be set during installation. Changing it later is possible, but requires access to the database through a non-Joomla medium or a Joomla Extension such as Akeeba Admin Tools and will cause some downtime.

Extension developers need to use the string #__ to represent the prefix. This will be replaced by the real prefix during runtime by Joomla.

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