A web application is a software application that can be run without being installed on the client and that has several parts: A part of it will run on the remote web server, another part will run on the client, usually inside a web browser. Both parts communicate over a computer network, for example the internet. The protocol they often use is called HTTP. This kind of application design is called client-server model. The parts are usually called "tiers". The most common kind is a three-tier application: One tier is called Presentation tier, another is called Application tier, and the third is called Storage tier. Common examples of web applications are those used for web mail, or for online banking. Social media sites, such as Wikipedia are also web applications. 