Joomla is a popular open-source content management system (CMS) that allows users to build and manage websites and online applications. It was first released in 2005 and has since become one of the most widely used CMS platforms in the world.

Key features of Joomla include:

1. **User-friendly Interface:** Joomla provides an intuitive and user-friendly interface, making it accessible to users of varying technical expertise.

2. **Extensions and Plugins:** Joomla offers a vast array of extensions and plugins that can be easily installed to enhance the functionality of your website. These include components, modules, templates, and languages.

3. **Templates and Themes:** Joomla allows users to customize the appearance of their websites using templates and themes, giving them control over the design and layout.

4. **Multilingual Support:** Joomla supports multiple languages, making it suitable for creating websites with a global audience.

5. **Content Management:** With Joomla, users can easily create, edit, and manage various types of content, including articles, images, videos, and more.

6. **Access Control:** Joomla offers robust access control features, allowing administrators to manage user permissions and control who can access certain parts of the website.

7. **SEO-Friendly:** Joomla is designed to be search engine friendly, helping websites rank better in search engine results.

8. **Community and Support:** Being open-source software, Joomla has a large and active community of developers, users, and contributors who provide support, resources, and updates.

Joomla is used to build various types of websites, including personal blogs, corporate websites, online stores (e-commerce), community and social networking sites, and much more.

As with any CMS, it's essential to keep Joomla and its extensions up to date to ensure security and functionality. Additionally, due to its open-source nature, it's essential to implement security best practices to protect your website from potential vulnerabilities.