A portion size describes *how the meal is sold* — e.g. Half Tray vs. Full Tray, each with its own price and container. A minimum quantity is a rule about *how many units a customer must buy at once*. Every catering portion size row on a meal (not just the default one) can carry its own Minimum Quantity, enforced when the item is added to the cart; the default catering portion's Minimum Quantity is additionally treated as the meal's overall minimum and is checked again at checkout against the meal's total quantity across all portions ordered that day.