Step 1: Understanding market equilibrium.
Market equilibrium occurs when the quantity of goods supplied equals the quantity of goods demanded at a particular price. At this point, there is no tendency for the price to change unless an external factor affects supply or demand.
Step 2: Evaluation of options.
- (A) Excess demand: Incorrect. Excess demand occurs when demand exceeds supply, leading to upward pressure on prices.
- (B) Excess supply: Incorrect. Excess supply happens when supply exceeds demand, leading to downward pressure on prices.
- (C) Deficient demand: Incorrect. This term is not used to describe market conditions at equilibrium.
- (D) Market equilibrium: Correct. This is the situation where market supply equals market demand.
Step 3: Conclusion.
Thus, when market supply equals market demand, the situation is called market equilibrium.
Final Answer: Market equilibrium.