Because you can't go to GoDaddy and ask to register http://local.dev3/ or local.dev3...
local.dev3 is the Base URL for the Virtual Host I created on my laptop.
These are "Domain Names"...
yahoo
google
sitepoint
sony
And these are "Top-Level Domain Names"...
.com
.net
.org
Of course, I was asking about the whole enchilda...
http://local.dev3/
http://www.MySite.com/
I am inclined to use the term "BASE URL" to answer my original question...
Debbie
It's still a domain name, it just doesn't use a TLD that is currently registrable.
You can make http://something.areallygnarlytld on your own machine if you want. It's still a domain name.