How do you trade in tower defense?

Excuse me, but I'm a bit confused. Tower defense is typically a genre of video games where players build towers to defend against waves of enemies. It's not a financial market or a tradable asset, so I'm not sure how one would go about "trading in tower defense." Could you perhaps clarify what you mean by this phrase, or if you're referring to a specific aspect of the cryptocurrency or finance world that I may have misunderstood?