The horizontal demand curve for a firm in a perfectly competitive market structure implies that the firm is a price-taker. This means that the firm cannot influence the market price and must accept the prevailing price set by the market. In this type of market, there are many buyers and sellers, homogeneous products, perfect information, and free entry and exit for firms. As a result, each firm's individual actions have no impact on the market price, and they can sell as much output as they want at the market price. Therefore, the demand curve facing an individual firm is perfectly horizontal, indicating that it can sell any quantity of output at the market price without affecting the price level.
