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What is a module?
A module is a set of PHP, JavaScript, and/or CSS files that extends site features and adds functionality. A set of Core modules is distributed as part of the core software download. Additional Contributed modules can be downloaded separately from the Download & Extend page on drupal.org.
What is an Experimental module?
An Experimental module is a module that is still in development and is not yet stable. Using Experimental modules on production sites is not recommended.
What are installing and uninstalling?
Installing a core or downloaded contributed module means turning it on, so that you can use its features and functionality. Uninstalling means turning it off and removing all of its configuration. A module cannot be uninstalled if another installed module depends on it, or if you have created content on your site using the module -- you would need to delete the content and uninstall dependent modules first.
Extending overview
See the related topics listed below for help performing tasks related to extending the functionality of your site.