Put simply, WordPress is a content management system. That means it has a hidden back door to the web site that can be accessed with a user name and password. Once you are logged into the back end or mission control or the dashboard, or whatever you prefer to call it, you control the front end of the site.
According to www.wordpress.org: “WordPress is a state-of-the-art publishing platform with a focus on aesthetics, web standards, and usability. WordPress is both free and priceless at the same time.”
According to wikipedia: “WordPress is a free and open source blog publishing application.”
Why WordPress, after all there are many other content management systems out there?
The short answer is: it’s easier to use than the other systems. People get up to speed with WordPress faster and get more out of it over the longer term. The worst outcome for a content management system is that people don’t get it when they first log in. They never get to first base and abandon the idea of managing their own web site.