This unfortunately does not have the world's simplest answer, but
luckily for you I am a Microsoft Certified Systems Engineer, and had
the same problem understanding the definition when I studied for my
Google.com and www.Google.com are both considered to be FQDN's or
Fully Qualified Domain Names. A FQDN must identify the server program
that an Internet request is addressed to. Just as confusing
unfortunately, I will back up a little and see if I can't make it
The Internet started with TLD, or Top Level Domains. There were
several types of TLDs.
The original 7 Generic TLDs:
.com, .edu, .gov, .int, .mil, .net, and .org
And the two letter Country Code TLDs:
.de, .jp, .mx, .ca etc etc...there are 240.
There was also .arpa which is considered an technical infrastructure
domain. For our discussion, this one can be left out.
These TLDs (Generic and Country Code) were created to simplify the
addressing of space on the Internet. It would be impossible to try and
remember the IP address of every website you enjoy, so they created a
simple folder structure to keep those addresses in an orderly fashion.
The easiest way to visualize the TLD structure is to use folder
structure, similar to the way folders on your hard drive, or folders
in your email program sort your information. The TLDs would be the top
folder. In your hard drive, that would be your windows folder, your
program files folder or your Documents and Settings folder.
On your hard drive it looks like this:
/Documents and Settings
Each of those folders are like TLDs. On the Internet they would look like this:
Now here comes the confusing part, they read right to left in the
address to relate to the folder structure to determine the address in
question. So for argument sake in the folder "COM", there is a folder
named "Google". So if you were trying to find the contents of Google
you would start by going in the "COM" folder, then look for the
"Google" folder. If the information or program you were seeking is in
that folder, then that is your FQDN. So, if you seek Google's main
search page, in /com/google you will find the default HTML page for
the home page. WWW is the default folder for the Google folder so it
is not neccessary to be named in a FQDN, however formally it can also
be used. So it would look like /com/google/www. If you were looking
for Answers on google, you would go to /com/google/answers or
/com/google/answers/www which is the home of answers.google.com or
www.answers.google.com either one is a FQDN as it is the exact fully
qualified domain name that takes you to the specific destination you
A non-fully qualified domain name is simple an incomplete address to
get you to where you are trying to go. For example, there is only one
FQDN Answers.google.com. Going to that address can only yield one
result. On the other hand, the domain level answers or answers.google
is not a fully qualified domain name as it can be hosted at many other
top level domains and sub domains.
Using answers.google as non-fully qualified domain name you can then
assume you might wind up at answers.google.monkey.com,
answers.google.net, answers.google.mil, answers.google.org. Because
there is no longer a single definitive TLD destination, your domain
name is no longer fully qualified.
I have left out a great deal of the history of the TLDs, specifically
that originally every fully qualified domain name ended in a trailing
For example: www.answers.google.com. would be a fully qualified domain
name because the finally trailing "." told the BIND DNS client library
that responded to that search that it could stop looking for a higher
level of that structure. If by some chance the BIND DNS client library
had a default it would take that on the end based on the lack of a
trailing ".". I left these details out, as they are outdated and would
only serve to confuse the subject.
Based on the amount of information that is being covered, the lack of
a true specific answer, and the answer being subjective to you and I
being able to find common ground for this discussion, I respectfully
request that you us the clarification option for any questions or
comments prior to rating this question which would allow me to give
more information to help clarify this subject for you.
[-- Mother911-ga --]