Final answer:
The Cournot model is used to analyze an oligopoly market where two firms choose their profit-maximizing level of output while assuming competitor's output is fixed. The reaction curve represents the relationship between each firm's output and the competitor's output.
Step-by-step explanation:
The Cournot model is a mathematical model used to analyze an oligopoly market where two firms produce at a constant average and marginal cost. In this scenario, each firm chooses its profit-maximizing level of output while assuming that its competitor's output is fixed. The reaction curve for each firm represents the relationship between its output and the competitor's output.