A  content management system or short CMS is a web application. A website built on a CMS software is a dynamic website. Such a website is driven by a database. The content  (data) is pulled from the database on demand.The content is separated from the template, in the administration section - so it is possible for non web designers / programmers to edit there content without coding or programming skills. Even new pages can be created on the fly.

Iin comparison to edit a static HTML based website you need some HTML and CSS knowledge or at least need to buy an advanced web design program like Dreamweaver..