Exploitability

If $ϵ=0$ then $\sigma$ is a Nash Equilibrium: no player has any incentive to deviate as they are all playing Best Responses.

If a game is two-player and zero-sum, we can use exploitability as a metric for determining how close a strategy profile $\sigma$ is to an equilibrium, ${ϵ}_{\sigma }$ where ${ϵ}_{\sigma }=b_1({\sigma }_2)+b_2({\sigma }_1)$ This will be important to measure how close the strategy profile $\sigma$ we generate is to the Nash Equilibrium.