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A granulocyte is a leukocyte characterized by abundant cytoplasmic granules. The major circulating categories include neutrophils, eosinophils and basophils. The term groups cells by characteristic morphology and related biology; it does not mean that every granule has the same contents or that every granulocyte performs the same immune function.^[ref]

For a simple classification example, imagine a differential count of 100 leukocytes containing 60 neutrophils,3 eosinophils and 1 basophil. The total is 64 granulocytes, not 60, even though neutrophils are the largest component in this invented sample. The example separates a broad category from its most numerous member; it is not a reference interval for a patient.

Morphology also should not be substituted for a functional measurement. S. D. Wright and S. C. Silverstein measured hydrogen peroxide release when human granulocytes and other phagocytes spread on surfaces bearing different recognition molecules. Surfaces coated with IgG produced a strong oxidant response, whereas C3b- or iC3b-coated surfaces did not produce appreciable peroxide release under the tested conditions.^[ref]

Thus the presence of granules or a capacity for phagocytosis does not by itself establish which signaling pathway was activated. Cell identity, receptor stimulation, uptake and extracellular release are different experimental variables.