This document discusses concepts related to revenue, including total revenue, average revenue, and marginal revenue. It provides the following definitions: Total revenue is the total amount of sale proceeds or receipts for a firm. It is calculated by multiplying price and quantity sold. Average revenue is total revenue divided by quantity sold and represents the average sale price per unit. Marginal revenue is the change in total revenue from selling one additional unit. Under perfect competition, price remains constant so average revenue and marginal revenue are equal. They form a horizontal line. Under imperfect competition, price falls as output rises, so average revenue decreases and marginal revenue lies below the average revenue curve.