Demand function a behavioral relationship between quantity consumed and a person’s maximum willingness to pay for incremental increases in quantity. It is usually an inverse relationship where at higher or lower prices, less or more quantity is consumed. Other factors which influence willingness to pay are income, tastes and preferences, and price of substitutes.
Demand function is a relationship between .a dependent variable and various independent variables. Like as-
Qd = f (P, I, T, H, Ms, Pr, S………. )
Qd = Quantity demand
P = Price
I = Income
T = Taste
H = Habit
GIs = Market size
Pr = Price of related goods
S = Social factors
So; demand function shows the relationship between quantity demand and other factors that affected quantity demand.