Ask someone for the 5-second definition of Zope, and you'll get "It's an application server." This is a true statement, but not a very helpful one if you're a manager charged with evaluating products that will become the framework of your company's web presence. If your web presence is small and fairly static, a web application server is likely not what you need ”you just need a plain ol' web server such as Apache.
Suppose that you decide to get fancy and use an interpreted language such as PHP, JSP, or even ASP to dynamically add a footer to each of your HTML files. Now you have a dynamic page and a very basic sort of web application. The only real difference between a website and a web application is that the web application has this sense of dynamism to it. It might be only one line of footer information, or it might be a change in the entire navigation set or color scheme of the template, but dynamic is dynamic. When you have created this sort of dynamic site, the web server that answers requests for pages has now become a web application server. It might be only a simple web server with, for example, the PHP parser built into it, or it might be something like Zope, which provides a developer with an entire application framework, not just a web server with a few add-ons.