A demand schedule is a table indicating various quantities at alternative prices. A demand curve is a graphical representation of the relationship. Everything, other than the price, that affects the quantity purchased is held constant. In the market for apartments this would include consumer income, population, the composition of the population, the price of houses, etc. Interpreting demand schedules and curves.
Demand represents a boundary for consumer behavior.
At a given price, demand indicates the most that would be purchased. Supply depicts the relationship between the price and the quantity supplied at each price, holding other things constant. A supply schedule is a table indicating various quantities at alternative prices. A supply curve is a graphical representation of the relationship. Everything, other than the price, that affects the quantity produced is held constant.