Monopolistic competition refers to a market with many sellers offering differentiated but similar products. Key characteristics include:
1) Large numbers of buyers and sellers, but less than perfect competition. Sellers offer heterogeneous products.
2) Products are differentiated through branding and perceived differences, allowing sellers some monopoly power as price makers.
3) In the short run, firms maximize profits where marginal cost equals marginal revenue. In the long run, free entry leads to normal profits as the market reaches equilibrium with excess capacity.