Apache module

Apache modules are extensions for Apache web servers that allow to extend the server’s functionality. There are two types of modules, the inbuilt (provided within the Apache core) and additional ones (optional, installed by server administrator if needed). The full list of modules can be found at the official website. For example, there are such popular modules as mod_rewrite that allows site administrators to use SEO-friendly URLs, mod_security that is used for improving site security by blocking the specific traffic, mod_pagespeed that improves site pages loading speed, etc. Feel free to check the Apache documentation to get more info.