The origins of dynamic pages

Most dynamic web pages are generated in response to queries run against databases. Behind your widget website there is a large database of widgets. When a visitor comes to your site and looks for left-handed blue widgets, it is this database that supplies the response. The database provides that information to the visitor. Typically the visitor checks a box or selects from a list or even types text onto the page and presses a "submit" button. Once she jumps through those hoops, your visitor gets her page full of left-handed blue widgets.