 extending and modifying your site functionality 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 drupalorg  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 additional resources concept modules drupal user guide  extending and customizing your site drupal user guide  