Joomla! is a free and open-source content management system (CMS) that is used to create and manage websites, blogs, and other online content. It is built using the PHP programming language and is based on a template system, which allows for easy customization of the site's design and layout. In terms of SEO, Joomla! has a number of features and capabilities that can be used to optimize a website for search engines:

Search engine friendly URLs: Joomla! can generate clean, search engine-friendly URLs for articles, categories, and other pages on your website, which can make it easier for search engines to crawl and index your site and also make it more likely that users will click on your links in search results.

SEO-friendly meta tags: Joomla! allows you to easily set up and manage title tags, meta descriptions, and other meta tags for articles, categories, and other pages on your site, which can help to improve the visibility of your site in search results and to increase the click-through rate for your pages.

Sitemap generation: Joomla! can automatically generate an XML sitemap of your site, which can help to ensure that search engines are able to find and index all of the pages on your site.

Plugins: There are many SEO plugins available for Joomla!, such as sh404SEF and JoomSEF, that can help to further optimize your site for search engines, such as by analyzing your content for keyword usage and helping to generate meta tags.

Speed optimization: Joomla! can be optimized for speed using a number of different techniques, such as caching, minifying code and using a Content Delivery Network (CDN), which can help to improve the overall performance of your site and make it more attractive to both users and search engines.

Mobile Optimization: Joomla! is mobile-friendly, which means that it can automatically adjust the layout of your website to fit different screen sizes and resolutions, this is important for the mobile search results.

Overall, Joomla! is a powerful and flexible CMS that can be used to create SEO-friendly websites. Its built-in features, along with the many available plugins, can help to improve the visibility of your site in search results, increase the click-through rate for your pages and optimize the site's speed. Keep in mind that even though Joomla! is SEO-friendly, it's important to have a proper SEO strategy and to regularly update and maintain your website to ensure that it remains optimized for search engines.