The Uniform Resource Identifier is used to refer to a specific resource (file/application/directory). These can be unique globally, or might be a relative indication. A URL is a globally unique location, which might be the location of a specific file, or the location of a specific host; this could, therefore, take the form of an IP address/socket or a domain name (for example, packtpub.com).

HTTP will generally split the URI into a relative identifier in the Request Line, and a host in the Request Headers.