Deadweight loss
A loss incurred due to inefficient planning or inefficient allocation of resources

Decreasing returns to scale
Where addition of a unit of input wouldn't result in the increase in the quantity of output

Deflation
A continued decrease in the level of prices in an economy.

Demand
The willingness and ability to buy something at a given price in a given point in time.

Demand-pull inflation
The increase in prices when caused due to increase in demand for goods

Demerit good
A good which is considered unhealthy for consumption by consumers.

Deregulation
The relaxation of government regulations in the economy or in an industry

Derived demand
When a commodity is demanded not because of a direct need for it, but because of its utility in the functioning of another product.

Diamond-water paradox
The factor that every commodity is priced according to its utility is not applicable in this case. Water which has more utility than a diamond is priced cheaper and the diamond on the other extreme.

Diseconomies of scale
A situation when a firm ceases to enjoy economies of scale on its production, and the cost per unit of production starts increasing.

Disequilibrium
A state of market, where there is a parity between demand and supply levels and they do not compensate each other