desktop vs top side

desktop and top side both are nouns.

Word	Noun	Adjective	Verb	Adverb
desktop	Yes	No	No	No
top side	Yes	No	No	No

As nouns, top side is a hypernym of desktop; that is, top side is a word with a broader meaning than desktop:

Other hypernyms of desktop include top, upper side, upside.

desktop (noun)	top side (noun)
(computer science) the area of the screen in graphical user interfaces against which icons and windows appear	the highest or uppermost side of anything
the top of a desk