Poop decks, located in the rear superstructure of the ship, belong mainly to the Age of Sail. Thus the poop deck is technically a stern deck, which in sailing ships was usually elevated as the roof of the stern or “after” cabin, also known as the “poop cabin”.
A poop deck is a high-up small deck that used to be used for navigational purposes. Modern cruise ships don't have poop decks because they are no longer needed, the Titanic was one of the last ships to have a traditional poop deck.