What is url?

URL 

URL

     URL (Uniform Resource Locator, previously Universal Resource Locator) - pronounced YU-AHR-EHL or, in some quarters, UHRL - is the address of a file (resource) accessible on the Internet. The type of file or resource depends on the Internet application protocol. Using the World Wide Web's protocol, the Hypertext Transfer Protocol (HTTP), the resource can be an HTML page (like the one you're reading), an image file, or any other file supported by HTTP. The URL contains the name of the protocol required to access the resource, a domain name that identifies a specific computer on the Internet, and a pathname (hierarchical description of a file location) on the computer.  

     On the Web (which uses the Hypertext Transfer Protocol), an example of a URL is:        
http://www.ietf.org/rfc/rfc2396.txt 
Which describes a Web page to be accessed with an HTTP (Web browser) application that is located on a computer named www.ietf.org. The pathname for the specific file in that computer is /rfc/rfc2396.txt.  
An HTTP URL can be for any Web page, not just a home page, or any individual file.  Examples: http://www.twitter.com
http://www.facebook.com
http://www.youtube.com