A CMS is a website software that builds dynamic pages from content saved in a database. This allows for easy updates to and maintenance of the site and greater flexibility than a static site.
Introduction to Content Management Systems
As applied to the web, a content management system (CMS) is an application that resides on the server. The CMS generates html pages to be served using a template for the page. The data from which the content is generated generally resides in a database.
Since most web CMSs are actually web based applications the management of these systems is usually accomplished through a browser based user interface. There are usually facilities within the UI that allow editing of the template and data entry.
Because the application is building the actual html pages that are served to a visitor there is little knowledge of html required. This makes it easy for non-technical people to build and maintain a website.
There are usually many templates available for the popular CMS products, both from the company producing the CMS and from third party suppliers. There are also usually plug-in applications to extend the functionality of the CMS, or to add custom features that are only needed by some users.
An advantage of a CMS is the ease of changing the information that populates the template. If you operate an online catalog you can change products or product descriptions easily. You can also add products to the database and new catalog pages will be generated.
Most eCommerce sites run on a CMS, and blogging software is a CMS optimized for blog content creation. Many websites are built on a CMS. More and more general sites are built on a WordPress code base because so many designers are familiar with WP.
Joomla and Drupal are leading open source CMS packages. Movable Type has an enterprise CMS package. OSCommerce is a CMS optimized for ecommerce.
There will be a learning curve if you wish to do complex things with these software packages, but once familiar with them it will be easy to accomplish your objectives. It is easy for non-technical people to add content and manage the CMS.