Uniform Resource Locators (URLs) are strings that specify how to access network resources, such as HTML documents. They are part of the more general class of Universal Resource Identifiers (URIs). The most important use of URLs is in HTML documents to identify the targets of hyperlinks. When using a Web browser such as Netscape, every highlighted region has a URL associated with it, which is accessed when the link is activated by a mouse click. Relative URLs specify only a portion of the full URL - the missing information is inferred though the context of the source document.
URLs are documented in RFC 1738. Relative URLs are documented in RFC 1808. URIs are documented in RFC 1630.
Here is a URL that describes the root page of the Internet Encyclopedia:
The meaning of these fields is as follows: