Demand
In economics, demand is the desire to own anything, the ability to pay for it, and the willingness to pay. The term demand signifies the ability or the willingness to buy a particular commodity at a given point of time. (Perkin, 1997) or
http://en.wikipedia.org/wiki/Demand

Economies of Scale
Economies of scale, in economics, refers to the cost advantages that a business obtains due to expansion. There are factors that cause a producer’s average cost per unit to fall as the scale of output is increased. "Economies of scale" is a long run concept and refers to reductions in unit cost as the size of a facility and the usage levels of other inputs increase. (Perkin, 1997) or
http://en.wikipedia.org/wiki/Economies_of_Scale