What is the difference between a URL and a URI?

With the advent and common use of the world-wide web, many people have become familiar with the "URL" acronym, which stands for Uniform Resource Locator. An URL, pronounced either as "earl" or by being spelled out, is used to identify a web page or other networked resource, such as a file accessible via FTP or an email address. What a URL does not specify is what information a networked resource should use to qualify any actions the resource might take. A Uniform Resource Indicator or URI, pronounced either as "ooree" or by being spelled out, allows for that. For example, http://www.google.com/search?q=test is an URI which tells Google's search engine what to search for by its use of a question mark and a name=value pair. Because of the question mark used for such URIs, everything after the question mark is referred to as the query line. In addition to allowing for query lines, however, URIs also encompass relative paths, # indicators and URNs, Uniform Resource Names, used to identify resources which may not or cannot be network accessible.

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