Wikipedia says the following:
In computing, the term remote desktop refers to a software or operating system feature that allows a personal computer's desktop environment to be run remotely on one system, while being displayed on a separate client device... Taking over a desktop remotely is a form of remote administration.
I think that Remote Administration covers remote-desktop. remote, remote-access.
I don't like the current description of remote-desktop - I personally feel that it should refer to GUI access only, not command line programs.
My preference would be to create a new tag of remote-administration and make them all synonyms of it, but I can understand why this might not be the prefered solution - in which case I would agree with Kaz and make remote-desktop a synonym of remote-access.