Can someone explain XenDesktop

[Pentoman]

I may, at unavoidably short notice, be supporting some Citrix Xendesktop kit.
I'm currently building and installing it on development servers but the problem is... I don't even know what I'm building or what precisely it will do.
I've struggled to find a competent explanation that isn't just marketing guff. You know what I mean - "virtualisation will transform your business!"
So, I'll keep building and figure it out but in the meantime, I know there are plenty of smart people here who can give a sensible technical explanation so I thought I would try.

Can someone just explain what it does and how.

I get server virtualisation.
I get windows terminal servers.
I get application streaming but haven't worked with it.
But primarily I'm coming from a background of old fashioned Windows terminal servers.

So what is XenDesktop? Seems like a weird hybrid of all three. If so, how does it work under the covers? Where do the boundaries lie? Does it provision virtual servers? Or just user profiles? Both? What can/can't it do? Agh! So much frustration!

[Pentoman]

Thanks all.

But how does it work?

I watched some tutorials and it appears you create a 'master image' (virtual machine). Then, when users connect in, they are spawned a clone. It's stateless and remembers nothing. Log off, it's deleted.

Did I get that right?