Mononuclear phagocytes are immune cells with a single nucleus involved in phagocytosis.
Histiocytes are a type of mononuclear phagocyte found in tissues, acting as macrophages.
Mast cells, basophils, and eosinophils are granulocytes involved in allergic reactions and parasite defense, but not mononuclear phagocytes.
Thus, the correct answer is Histiocyte.