Granulocytes are a category of white blood cells characterized by the presence of granules in their cytoplasm.

They are also called polymorphonuclear leukocytes (PMN, PML, or PMNL) because of the varying shapes of the nucleus, which is usually lobed into three segments. This distinguishes them from the mononuclear agranulocytes. In common parlance, the term polymorphonuclear leukocyte often refers specifically to neutrophil granulocytes, the most abundant of the granulocytes; the other types (eosinophils, basophils, and mast cells) have lower numbers. Granulocytes are produced via granulopoiesis in the bone marrow.

Neutrophils (also known as neutrocytes) are the most abundant type of granulocytes and the most abundant (40% to 70%) type of white blood cells in most mammals.