What is the difference between a website and a web application?

Although websites and web applications make use of similar technologies, and share many fundamental parts their primary difference is a website is designed primarily as an advertising/selling tool on the internet. A web application is a tool or piece of software just like any other piece of software you run on your computer that is designed using the same web technologies as those employed by web sites and viewed over a web browser. The advantage here is that you can always use this software wherever you have access to the web server (ie any internet enabled computer). An example of a very popular web application is Outlook Web Access. If you are running an Exchange server you can run Outlook inside Internet Explorer and from any Internet cafe computer or your home computer easily gain access to your work email!