A relative URL with only a file name links to a file in the same folder as the current page.
Relative URLs are shorter—they don't contain every part of the URL syntax. For the parts of the syntax that aren't specified, the browser uses the parts of the current page. This is why they are called relative URLs, because their location is relative to the current page.
For example, one of the most common relative URLs only has a file name, like this:
In this case, the browser assumes that the missing parts of the URL syntax (the protocol, server name, and path) are the same as the current page. All it has to do is find the "default.htm" file in the same folder as the current page. For a visual example, take a look at the illustration on the left.
Relative URLs are really handy for two reasons. They are shorter and therefore easier to use when inserting hyperlinks in your Web pages. And, most importantly, if you end up moving a group of pages, then you don't have to change all of the URLs if the pages are in the same, relative position to each other. Consequently, you should always use relative URLs to link to pages within your Web site.