Dynamic web sites are driven by programs that run on the web server to make the page "live." These programs can do simple things like rotate image links on a web page, or very complex things like managing a discussion forum, a shopping cart or a content-management system.
When developing a dynamic web site, sometimes the business goal may be satisfied by installing and customizing already written programs. For many organizations, use of off-the-shelf software is not sufficient. In such cases, then programs must be written to the organization's business specifications.