What is a url adderess

It is the entire address of a website. For example, the URL of this webpage is

http://wiki.answers.com/Q/What_is_a_url_adderess&action=edit

if you click on it, it will take you directly to this page.

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URL stands for "Uniform Resource Locator".
As mentioned above, a URL could point to a specific page, or it could just point to a site such as http://wiki.answers.com

Once a URL is entered, it is cross-referenced using DNS (Domain Name Service) to an IP address (Internet Protocol). For example, when you type http://wiki.answers.com your computer is actually going to http://192.41.64.25 The http: means "Hypertext Transport Protocol" and is the language of web pages.