Let me ask a different question.  Do you care whether the box of rags is in the basement, attic or garage?  No, as long as you know where you left it and can get to it  easily when you want a rag.

 

Now, why would you care where your word processing program is?  Do you care if it is in memory, a hard drive, a CD or an external drive?  You don't.  Or you should not, as long as you can get to it easily.  It is as unimportant as where you left the rag box.

 

Thin Clients are computers that store the programs, the applications, not on the hard drive, but elsewhere, in this case somewhere on the network.  The elsewhere is an Application Server, which is simply a box storing programs for others to use. 

 

 Thin Clients are called "thin" because they do not have to store the applications.  Let's see, a regular desktop computer has to store five gigabytes for Office, forty gigabytes for Vista, another 60 for the new browser, and so on and so forth.  Storing all that stuff makes a computer fat, also more expensive and slower, more prone to problems from viruses and disk failures, and so forth.

 

Why the confusing names?  Simple, you could not get as much money selling a simple little computer, the thin client, and a box for putting applications in.  But that is all they are, a simpler computer, the client, and a box for putting applications in, a server.

 

Now when someone talks to you about thn clients and application servers, you can just say to them, "Doh!  What dumb names for a simple computer and application storage box." 

 

Besides it is not new, not at all.  The principles were done on mainframes back in the late 1960's.  See the history page for more info.