What is the result when you derive the Gross Profit with respect to Quantity. I know Marginal Revenue is derive

What is the result when you derive the Gross Profit with respect to Quantity. I know Marginal Revenue is derive

Revenue w.r.t quantity. But not sure what deriving Gross Profit w.r.t Quantity does. (side note: i am currently working on game theory with cartel and they have gross profit, so I am just wondering why derive Gross Profit, like what does that result in)