A web page (or entire website) is referred to as Dynamic when most, if not all, of the content is actually stored on an online database, and the visible content is only displayed on demand following a request for a specific item or data by the end user. The end user's request usually takes the form of clicking a specific link or button, typing in a search phrase, or selecting items from a list.

These days most of the product displays for ecommerce shopping sites are fed dynamically from an online database, particularly if hundreds of products are involved. As the site owner has access to the online database at any time 24/7, this makes it easy for the site owner to keep products and prices up to date and fresh, and remove loss-making or redundant products. As soon as a product has been updated or a new one added, the new data is immediately visible on the website. 

This is extremely powerful as it enables the site owner to keep the website as fresh and up-to-date as a physical display in a shop or store.  Thus the latest products and prices are instantly visible worldwide.

Dynamic, database-driven sites also have other uses. Many information and news sites store their articles in online databases, serving the visible page dynamically when requested by the end user. This is also true of Weblogs, which also rely heavily on databases for storage and feeding their blog content on demand.

Generally speaking, a dynamic, database-driven website is initially more expensive than a conventional static website, but can prove more economical in the long run.  Owners of static websites will need the services of their web designer every time they want to make changes and updates, whilst dynamic website owners are able to make most of the changes themselves.