URLs
A URL specifies the location of networked resource--a file, for example.
A common URL is one for a web resource:
Other protocols are possible:
Host Name -- the name of the machine ‘hosting’ the resource
Filename -- the pathname to the file on the host
Port Number -- the port number to which to connect (optional).
Reference -- a reference to a named anchor within a resource that usually identifies a specific location within a file (optional).