Glossary:
Joomla
Joomla is a Content Management System and MVC web development framework for managing web sites. Joomla can be used to manage websites from simple blogs to corporate websites.
Joomla is free open source software and is cross-platform so it can run on many web servers setups.
Joomla is written in PHP and as such requires a web server with PHP running and a database (usually MySQL).