WordPress is a free and open-source content management system (CMS) based on PHP and MySQL. To function, WordPress has to be installed on a web server, which would either be part of an Internet hosting service or a network host in its own right. An example of the first scenario may be a service like WordPress.com, and the second case could be a computer running the software package WordPress.org. A local computer may be used for single-user testing and learning purposes.
More information: https://en.wikipedia.org/wiki/WordPress