Uniform Resource Locator
Most commonly used to find resources on the World Wide Web, but much more general in capability, a Uniform Resource Locator (URL). Their syntax is:
A URL contains the name of the scheme being used (<scheme>) followed by a colon and then a string (the <scheme-specific-part>) whose interpretation depends on the scheme. 
Primary WWW usage
commonly refers to a link on the World Wide Web. URLs usually start with http://, e.g. this page's URL is http://en.citizendium.org/wiki/Uniform_Resource_Locator. In this example, the en.citizendium.org is a DNS name.
Direct IP protocol request