URL stands for Universal (or Uniform) Resource Locator.
In Layman's terms, a URL is a web address (or a network address).
These are all in the same domain (yourdomain.com), but all three have different URLs.
If you are asked to include a URL in a support request, make sure you do not confuse that with a domain name, e.g yourdomain.com
URLs typically refer to a domain name + other information. "other information" means http:// or http://www. plus the domain, or in other circumstances, http://subdomain.yourdomain.com or even http://yourdomain.com/something/file.jpg
URLs can be thought of as a more specific term than simply a domain name.
It helps us to troubleshoot if you include the exact URL to whatever error you might have. If you submit a trouble ticket like:
"The pages on my site do not work" We will at the least, ask you for a domain name. (yourdomain.com)
But more than likely, you would be asked for a URL. The URL will be the specific web address to the problematic web page, or image. (http://yourdomain.com/whatever/is/broken.php)
Remember, http://yourdomain.com and http://www.yourdomain.com might be the same place on your site, but that is not the case for many sites, so presenting us with the exact URL will help every one to be on the "same page," so to speak.