Modules are the most complex form of ExpressionEngine Add-On. They can have their own database tables, backend control panels, tabs and fields that are included on the publish page, as well as their own tags for use in templates.

Modules are the most complex form of ExpressionEngine Add-On. They can have their own database tables, backend control panels, tabs and fields that are included on the publish page, as well as their own tags for use in templates.

Ref. http://ellislab.com/expressionengine/user-guide/development/modules.html