A portion is a quantity of food served to or intended for one person, the practical unit by which meals are divided, costed, and nutritionally assessed. As a verb, to portion is to divide bulk food into such individual servings. The concept sits at the heart of food service economics, where portion control determines food cost percentages, and of nutrition, where portion size powerfully influences intake: larger portions drive greater consumption almost unconsciously, a phenomenon called portion distortion as commercial servings have grown over decades. Dietary guidance increasingly expresses recommendations in portion terms, handfuls, cupped hands, and everyday objects, because few people weigh food. For caterers, consistent portioning ensures fairness, cost control, and accurate allergen and nutrition information; for eaters, awareness of portions is among the simplest weight-management tools.