refer to http://www.iis.net/learn/get-started/planning-your-iis-architecture/understanding-sites-applications-and-virtual-directories-on-iis
IIS 7 and above formalizes the concepts of sites, applications, and virtual directories.
Briefly, a site contains one or more applications, an application contains one or more virtual directories, and a virtual directory maps to a physical directory on a computer.
A site is a container for applications and virtual directories, and you can access it through one or more unique bindings.
Windows Process Activation Service (WAS)
Windows Communication Foundation (WCF)
Transmission Control Protocol (TCP)
Microsoft Message Queuing (MSMQ)
In addition to containing applications (which contain virtual directories) and specifying bindings, the following configuration settings belong to the site:
- Limits: configure settings to limit the amount of bandwidth, the number of connections, or the amount of time allowed for connections to a site.
- Logging: configure settings for handling and storage of log files for the site.
- Failed request trace logs: configure settings for logging failed-request traces for the site.
An application is a group of files that delivers content or provides services over protocols, such as HTTP. When you create an application in IIS, the application's path becomes part of the site's URL.