Joomla is an Open Source Content Management System (CMS) which can be divided into two parts as Open Source and Content Management System. Open source is a concept that basically involves allowing a community to develop and improve a piece of software. The Joomla community do what they do to make the web a better place.
Content Management System is a piece of software that runs on a server and displays a website to your browser when you request it. It allows the page you see to be dynamic (it can change depending on what you're doing) and it allows the owner of the site to make changes to the way the site looks without changing the 'code' behind the site.
In addition to being a full-featured CMS, it is easy to learn, quickly to set up, and Inexpensive. Joomla is a community developed piece of software that allows almost anyone to manage and update their own website. Joomla's extensive third-party development community has created thousands of plug-ins, extensions, templates, and other options to empower you to make the most of your site without having to be an expert in Web development.
Rocket Theme, for example, provides a number of useful and freely-available templates and extensions for Joomla while creating premium templates and applications for anyone wanting to kick their site up a notch without spending large amounts of time and money to do so.
Joomla Provides plug-ins and site modules to enhance website and its content and over 6000 extensions available
Responsive templates adapt websites for various platforms including all mobile devices.
Joomla Supports for different languages for different sites.
It also supports polls, search and web link management.
Corporate Web sites or portals
Corporate intranets and extranets
Online magazines, newspapers, and publications
E-commerce and online reservations