What term describes a decrease in white blood cells?

Leukopenia is the correct term for a decrease in white blood cells. White blood cells are a crucial part of the immune system, helping the body to fight off infections and diseases. When the level of these cells drops significantly, the body's ability to combat infections can be impaired, leading to increased susceptibility to illness.

Leukocytosis, by contrast, refers to an increase in white blood cell count, usually as a response to infection, inflammation, or other stimuli in the body.

Anemia is a condition characterized by a deficiency of red blood cells or hemoglobin, which can lead to fatigue and weakness but does not directly relate to white blood cell counts.

Hemophilia is a genetic disorder affecting blood clotting due to the absence of certain clotting factors, which is unrelated to white blood cell levels.

Thus, the terminology associated with leukopenia specifically addresses the reduction of white blood cells, making it the correct choice for this question.