Most computers on the internet have a single internet address; however, often via special kernel patches, a given computer can be made to respond to several ip addresses and provide different services (typically different web services) on each. Each of these different IP addresess (which generally each have their own hostname) act as if they were distinct hosts on distinct machines, even though they are actually all one host. Hence, they are virtual hosts. A common use is when an internet service provider "hosts" world-wide web or other services for several of their customers on one computer but giving the appearence that they are separate servers.