In a market where two companies compete on pricing, if neither company can benefit from changing their prices while the other's price remains unchanged, which concept is illustrated in this scenario?

The situation described is called a Nash equilibrium. In this case each company’s price is the best response to the other company’s price, so neither can improve its profit by unilaterally changing its price. Because every company is already doing the best it can given the other’s choice, no one has an incentive to deviate. For example, if two firms set a price of $10 and neither can gain by lowering to $9 while the competitor keeps $10, the $10 price pair is a Nash equilibrium. This concept shows how stable strategies arise in competitive markets.