Apache modules are pieces of software that extend the functionality of the Apache HTTP server. They can be used to add new features, such as support for different file types or authentication mechanisms, or to improve the performance of the server. To check which modules are loaded, use the following command:
$ apachectl -t -D DUMP_MODULES
This will print a list of all the modules that are currently loaded, along with their status. If a module is not loaded, it will be listed as “disabled”.