What is a Resource Identifier in the Restful architecture?

Every Resource on the Server needs to be uniquely identifiable. To do that every resource has a unique URL that can be used to get to that Resource.

URL: http://example.com/utilities/locationutil/mylocation

You can see that to access your location you have to hit the above URL. Here the Resource is your location while the unique way to access it is the Resource Identifier (URL).

Important point to note here is that a resource is not necessarily a static piece of information. For example this URL when hit by someone from United States will give their location while when hit from India will give some location from India. The location is calculated at run time and sent back to the Client. Even a dynamic information is also called a Resource.