Demand refers to consumers’ willingness to purchase goods and services at given prices. 
The Law of Demand states that quantity purchased varies inversely with price. The higher the price, the lower the quantity demanded. 
A demand curve (more formally known as a demand schedule) is a mathematical function or graphical representation of the quantity demanded for a product at different prices, all other things being equal. 
Demand schedules are used in marketing to help determine the price point for a product given sales and margin goals.
Although it is customary for P to appear on the Y-axis and Q on the X-axis in economics textbooks, it is also the usual practice in science to represent the independent variable (price, in this case) on the horizontal (X) axis. 
Linear demand occurs when each increment in price reduces the quantity consumers are willing to purchase by an equal amount. 
A constant elasticity demand curve has a constantly changing slope with the underlying assumption that a small percentage change in price causes the same percentage change in quantity, regardless of the initial price. 
A demand curve can be shifted outward by increasing brand preference. Management can then choose to sell the same quantity of branded products at a higher price, a higher quantity at the same price, or some other combination of these along the new demand curve.  (see MASB video: Five Compelling Reasons for Brand Preference)
Maximum Reservation Price: The lowest price at which quantity demanded equals zero. Above this price, no customer will buy the product.
Maximum Willingness to Buy: The quantity that customers will “buy” when the price of a product is zero. This artificial concept is used to anchor a linear demand function.
- Common Language in Marketing Project, 2021.
- Paul A. Samuelson, Economics: An Introductory Analysis; New York, 1967; pg 59.
- Farris, Paul W., Neil T. Bendle, Phillip E. Pfeifer, & David J. Reibstein (2010). Marketing Metrics: The Definitive Guide to Measuring Marketing Performance (Second Edition). Upper Saddle River, New Jersey: Pearson Education, Inc.