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I'm confused in the actual meaning of domain. Is the domain mean any web page address like "superuser.com" or its actual meaning is the name of network which provides internet connection.

Thank you.

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4 Answers 4

A domain name is nothing more than a name we humans use to connect to a specific IP address. When you type in a URL your browser splits this into different parts. The domain name (superuser.com in this case) really only means something to you at this point. Your computer will use DNS (Domain Name System) to turn that domain name into something it can understand, an IP address. Once your computer has the IP address of the server, it can communicate with that server to accomplish its task, such as sending an HTTP GET to download a web page, etc..

Subdomains (the www. in www.microsoft.com or mail. in mail.google.com) work in the same way except that they allow the network administrators to split out names to different servers (or the same server if they want). This allows the administrator to say that 64.4.31.252 will handle www.microsoft.com and 64.4.11.251 will handle msdn.microsoft.com.

Other technologies do rely on DNS to work as well, so it isn't always "just for humans" (though that's how it started). Certificates for websites (using HTTPS and SSL) rely heavily on DNS to work, since that's one of the major checks that help prevent phishing. Certificates can contain the DNS name of the site they protect and if they don't match your browser will scream bloody murder and let you know that "there is a problem with this site's certificate". You can see this for yourself if you visit https://209.85.225.105 (that's an IP for www.google.com, you can look this up yourself by running nslookup www.google.com from the command line.

DNS originally came about to help people connect to remote sites. It's much easier to say (and remember!) "go to www.google.com" than it is to say "go to 209.85.225.105".

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It should perhaps be noted that Microsoft refers to Active Directory structures as "domains" as well. So, when someone refers to an "AD domain", they are referring to an Active Directory tree or forest, which is completely unrelated to internet browsing. (Active directory is Microsoft's centralized authentication and management system.)

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The domain is not just ANY webpage in the URL sense, but specifically the top level root naming/identification of the webpage that human beings can relate to - it really serves as an identification (or a brand almost) for any of the pages that live under it (as perceived by the visitor of the webpage). There's a whole registration system for domains, and each domain is unique.

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In an URL the two rightmost parts - in superuser.com these are "superuser" and ".com" are called domain and top level domain (TLD).

Wikipedia has an article on top-level domains, and domains need to be registered to be known.

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