|Pretty much what they sound like, actually. A Desktop, in this context, is a workstation computer (as opposed to a server).|
An unmanaged desktop is just a PC running local apps and OS without being centrally controlled, as in a domain.
A managed desktop is the opposite. A PC that may be running local apps and OS, but that is also centrally managed or controlled. Means of control would be logon scripts, domain group policies, antivirus definition distribution, etc.
Hope you get an "A"!