If you receive emails or emailed forwards or if you notice ads on websites you may wonder where it comes from. This website lists alphabetically those two letter abbreviations on the end of URLs.
Now, thanks to Art Gorski we learn more: "Actually, that website doesn't list 'URL's, it lists the codes for the Top Level Domains (TLD). The second, third, and so on 'levels' are listed to the left of the TLD in each URL, separated by periods. So in www.pmug.us, us is the TLD, pmug is the second level (everything at PMUG), and www is the third level (the web server at pmug). You could have other third level devices, like a server at server.pmug.us for example.
"A fun thing to do with TLDs is to purchase a personal domain for yourself. For instance, I've thought about getting 'art.gors.ki'. Just because I don't live in Kiribati doesn't mean I can't own a domain name registered there. ;-)"