I'm not sure what the popular term is for these things, but on the official Ubuntu website they appear to use "edition" for the various formulations of the main distribution.
I think in the past Ubuntu Netbook was also known as the "Netbook Remix".
I'm interested in hearing the view of other people on the most useful way of tagging questions specific to the various editions.
Desktop Edition
The desktop edition appears to be mostly tagged as ubuntu-desktop. There were previously two questions tagged desktop-edition but I retagged them to the former tag because it was more common.
(There are also a significant number of questions tagged desktop but it isn't clear to me how many of those use the tag to mean the Desktop Edition.)
Netbook Edition
There are quite a few tags that refer to the Netbook Edition. The most common tag appears to be netbook (but at least two of those questions refer to the netbook edition of the Kubuntu derivative). The second most common appears to be une.
I think the unr tag is supposed to be remapped to ubuntu-netbook-remix as a synonym but I'm not sure if it is working quite right at the time of writing this.
Server Edition
Questions about the Server Edition appear to be tagged with ubuntu-server. There were some questions tagged server-edition but I changed those to ubuntu-server because it was more common. There is also a server tag and many (or possibly all) of those questions are about the server edition as well.