I've done some quick google searches for glossaries and such to explain the differences of domain mapping, masking, and mirroring, but I haven't come up with a resource explaining them all. This is not my particular domain (ha!) so I'm not sure if it's essentially OK to use domain mapping and domain masking interchangeably.

Specifically I want to use the term which defines, as precisely as possible, the scenario of having x number of servers named www1.foo.com, www2.foo.com, www3.foo.com, (etc) all reporting to the user as www.foo.com

My gut instinct is to say masking, but I've heard mapping as well. Thanks metachatters for being more well informed than I.

Easy-peasy. It's known as subnet addressing.

Hmmm, it doesn't seem to me that "subnet addressing" describes what safetyfork is asking about, and the article you linked doesn't seem to describe it either, although I admit I skimmed it.

safetyfork wants to know how to have multiple servers that respond to one URL, right safety? Or more specifically, wants to know what the practice is called.

Round-robin DNS is one basic technique that will achieve this.

"Domain Mapping" appears to describe making something like agropyron.typepad.com redirect to agropyron.com.

"Domain Masking" appears to describe a technique for hiding the domain name of a site. Like I could have agropyron.com display the content from foobar.com, but hide the url of foobar.com from the users.

From the server-side, you're talking about Domain Rewriting, or from the users' side, Many-to-One DNS Resolution...

I haven't fully read the links yet (just got back to being able to look here -- sorry for the delay things got out of hand elsewhere), but I'm looking for the words that describe having multiple servers report as one domain, for instance one server (www1) would have directories a,b,c - while another server (www2) has directories p,d,q - and yet another server (www3) has directories x,y,z but the user sees/navigates just www with directories a,b,c,p,d,q,x,y,z.

So from what I've just seen form the responses here that's doing what I guess would be Many-to-One DNS Resolution which could be achieved by either Round-robin DNS or Domain Rewriting perhaps?

Thanks benzo8, agropyron, and Smart Dalek.