When a user navigates to a website by using the address bar of the browser or by clicking on a link in a page, the browser sends an HTTP GET request, with the URI specified in the address field or in the link element, such as http://hostname.domainname:8080/dir/file?arg1=value1&arg2=value2.
This address is commonly named Uniform Resource Locator (URL) or Uniform Resource Identifier (URI). The difference between these two acronyms is that a URI is something that uniquely identifies a resource without necessarily specifying where it can be found; a URL, however, specifies exactly where a resource can be found. In doing this, it also identifies the resource because there can be only one resource in a single place.
So, every URL is also a URI, but an address can be a URI without being a URL. For example, an address that specifies the pathname of a file is a URL (and also a URI) because it specifies the path to the file. However, an address specifying...
