Possible Duplicate:
What's the difference between a URI and a URL?
Just to get it right:
URI = Tells you in which hotel you should go to sleep.
URL = Tells you in which room in what hotel you should go to sleep.
So URL is a lot more specific, it points to a final destination. The thing you want. While URI is something strange.
So what exactly is URI when it's not an URL? What's the real difference?
Answer
URI: Uniform Resource Identifier (URI) is a string of characters used to identify a name or a resource on the Internet. Such identification enables interaction with representations of the resource over a network (typically the World Wide Web) using specific protocols
URL: In computing, a Uniform Resource Locator (URL) is a subset of the Uniform Resource Identifier (URI) that specifies where an identified resource is available and the mechanism for retrieving it.
Example
To identify a specific resource and how to access it - in all completeness
URI: mysql://localhost@databasename:password
The URL shows you where you can find the database on the internet and which protocol you should use.
URL: mysql://localhost