WordPress exists as both a platform and an open source software project.

This entry is for the platform, which is less flexible than the software project, but comes with the benefit of being run on servers that you don't have to manage. You still have access to some plugins and plenty of templates, and have some different functionality as well, like being able to take advantages of certain services that the WordPress company, Automattic, provides.

It is a powerful system with a strong ecosystem, lots of plugins, templates, and more.