Aplastic anemia is a condition where bone marrow does not produce sufficient new cells to replenish blood cells.
The term 'aplastic' means the marrow suffers from an aplasia that renders it unable to function properly. Anemia is (per definition) the condition of having reduced hemoglobin concentration in the blood. Typically, anemia refers to low red blood cell counts, but aplastic anemia patients have lower counts of all three blood cell types: red blood cells, white blood cells, and platelets, termed pancytopenia.