Final answer:
A perfectly elastic supply curve is horizontal, indicating infinite responsiveness to price changes at a specific price level, supplying an unlimited quantity at that price but none if the price deviates.
Step-by-step explanation:
A perfectly elastic supply curve is horizontal. This represents a situation where the quantity supplied is infinitely responsive to price changes. Specifically, at a certain price level (P), producers are willing to supply an infinite quantity of goods, but if the price moves away from this level, the quantity supplied drops to zero. This is in contrast to the perfectly inelastic supply curve, which is vertical and indicates that the quantity supplied does not change regardless of the price. Perfect elasticity is an extreme and theoretical concept demonstrating a situation where suppliers are fully responsive to any change in market price.