|Picture of the month!!!|
Must I clarify again! Skin is your operating system's GUI(graphic user interface)
(as in windows xp's blue or vista's Aero)
not your skin!!!!
shell is format that allows you to interact with your system kernel services. Either through command line or GUI.
so when it's asking shell, it could be referring to the many distributions of linux, a version of windows, or mac.
That is what deviantart is asking.