Modules extend the capabilities of Joomla! giving the software new functionality. Modules are small content items that can be displayed anywhere that your template allows it to be displayed by assigning them to positions and pages through the module manager in the administrative interface.
Modules are installed in the Admin Section. Joomla! modules may include: Main Menu, Top menu, Template Chooser, Polls, Newsflash, Hit Counter, etc.
Members of the Joomla! Community produce Joomla! modules on a continuous basis.