Uniform Resource Locator (URL) is a technical, Web-related term used in two distinct meanings:
In popular usage, it is a widespread synonym for Uniform Resource Identifier (URI) — many popular and technical texts will use the term “URL” when referring to URI;
Strictly, the idea of a uniform syntax for global identifiers of network-retrievable documents was the core idea of the World Wide Web. In the early times, these identifiers were variously called “document names”, “Web addresses” and “Uniform Resource Locators”. These names were misleading, however, because not all identifiers were locators, and even for those that were, this was not their defining characteristic. Nevertheless, by the time the RFC 1630 formally defined the term “URI” as a generic term best suited to the concept, the term “URL” had gained widespread popularity, which has continued to this day.
via the wonderful Wikipedia