WordPress is a popular open-source content management system (CMS) that is used to build websites and blogs. It is based on the PHP programming language and uses a MySQL database to store data. WordPress is known for its ease of use and flexibility, which makes it a popular choice for creating a wide range of websites, from simple blogs to complex e-commerce sites. It also has a large community of users and developers who have created a wide range of plugins and themes (templates) to extend its functionality. It is also known for being SEO friendly and easy to customize.