Which of the following is NOT a type of leukocyte?

The correct choice identifies a term that does not represent a recognized category of leukocytes. Granulocytes, lymphocytes, and monocytes are established classifications of white blood cells involved in various immune responses.

Granulocytes, which include neutrophils, eosinophils, and basophils, are characterized by their granules in the cytoplasm and play a significant role in inflammatory reactions and combating infections. Lymphocytes are crucial for adaptive immunity, with subsets such as T-cells and B-cells that protect against specific pathogens. Monocytes, which develop into macrophages and dendritic cells upon entering tissues, are essential for phagocytosis and activating certain immune cells.

The term "eosinocyte" is not commonly used in the literature of hematology and does not classify leukocytes. While eosinophils are a type of granulocyte characterized by their affinity for eosin stains, "eosinocyte" lacks usage in clinical or scientific contexts, making it the outlier among the choices given.