What is the Cournot model of oligopoly? What do Cournot markups mean?

Under the market structure of oligopoly, it is accepted that there are a few firms that produce an item (service or good) and the cost of the item will depend on the amount produced. The Cournot model makes a supposition that rival firms produce a homogenous item, and each firm endeavors to boost profits by choosing how much to produce. All organizations may choose their production level at the same time. The essential supposition of the Cournot model is that each firm will be choosing a quantity, given the quantity that its rivals choose. The resulting equilibrium is a Nash equilibrium in quantities, which is known as the Cournot (Nash) equilibrium

As per the Cournot model, where there are a number of competitors producing homogenous goods, the bigger the market share of a firm, the higher is the markup over its marginal cost/price. The market demand for this firm is also less elastic. This is the pricing practice followed by a producer with market power.