the word acts as a replacement for nouns and general abstract "things" you just can't remember their definitions. usually its not that there is no word to express the certain noun, for example, "chair", but at the moment of creating the grammer of the whole sentence, it slips out of your mind. that's where "Shlingy" comes along. Its resembles the English use of "Thingy" in a sentence.
someone: Hey dude, can you pass me the shlingy?
dude: Which Shlingy, Salt Shlingy or katchup Shlingy?
someone: Shlingy Shlingy *Points at juice*
*dude passes the Juice*
someone: You see, the whole structure is comprised of tiny... umm... tiny Shlingies...
someone else: I see......