Content Management Systems
The notion of a content management system is these days what we understand a website to be. The old days of HTML, MAS FrontPage, and the like have slipped on by. With a Content Management System the structure of the Website is contained within a System Engine and a Theme (or some such similar name depending on the system) and a database with the content. When a visitor visits the site the system looks up the database and delivers the content based on their choices.
The updating of the content is normally driven from a back-end password secured portal that lets the user add and edit content to be displayed on the site.
There are a great many such systems, and the one I almost exclusively work with is WordPress, which actually powers about 25% of all websites, and is powerful enough for most purposes, yet easy enough for people to be able to manage and update content.