What is the rarest game in the world?

Can you elaborate on what exactly constitutes the "rarest game in the world"? Are we referring to physical games that are scarce in quantity due to limited production runs, such as rare vintage arcade machines or collector's edition board games? Or are we talking about digital games that are exceptionally difficult to obtain, perhaps due to exclusivity agreements or simply because they're no longer available for purchase? Additionally, how do we measure rarity in this context? Is it purely based on scarcity, or does it also factor in the game's historical significance, cultural impact, or even its gameplay quality? Understanding these nuances could help us arrive at a more comprehensive and accurate answer to this intriguing question.