A particular glycoprotein may occur in forms that differ in the structure of one or more or its carbohydrate units, a phenomenon known as microheterogeneity.
Sources:
PAC, 1988, 60, 1389. 'Nomenclature of glycoproteins, glycopeptides and peptidoglycans (Recommendations 1985)' on page 1391 (https://doi.org/10.1351/pac198860091389)
White Book, 2nd ed., p. 86 (https://iupac.qmul.ac.uk/bibliog/white.html)