Joomla is a Content Management System which is free and open source to design websites easily. To add extra features in Joomla which are not available we need to extend it using extensions. Extensions role is to add some extra functionality to the Joomla according to requirement of the website. There are five types of extensions:

Components:

Components work as a mini applications in Joomla which is the most complex extensions. Most of the components in Joomla contains two parts: a site part and administrator part. Whenever you make request for a Joomla page one component render that page. For example: com_content component handles the display of the content; com_users handles the display of the users and so on.

Modules:

Modules are used to render the page. They are lightweight and flexible extensions. Modules are the small sections or boxes that are placed around the component. Modules are assigned per menu item i.e., you can hide or display module.

Plugins:

Plugins are the type of Joomla extensions which are associated with trigger events. Joomla have a set of plugins. Whenever any event occurs all the plugins related to that are executed in sequence.

Templates:

Templates are extensions which represents how the site look. It is basically the design of the site. In Joomla, two types of templates used: one is front-end templates and other is Back-end templates. Front-end handles the website looks and the back end handles the website's administrative task. It have some fields in which modules and components shown.

Languages:

These are the basic extensions. It can be packaged in two ways: core package and as as extension package both are consist of key/value pairs.