Joomla!® lets you use Search Engine Friendly (SEF) URLs for your website, which can help improve your search engine ranking.
Simple changes, such as installing new modules or plugins to the Joomla configuration, can trigger common issues with SEF URLs. You can troubleshoot your Joomla SEF URLs by disabling and then re-enabling them. If you need more information, see Enabling Joomla! Search Engine Friendly URLs.