Modifier
A modifier is an option attached to a menu item that changes its price, its preparation or both: the large, the no onions, the extra cheese, the half and half. Modifiers are where every real menu stops being a simple list, and they decide whether a till or an ordering system is pleasant or infuriating to use. A good model handles free options, paid options and mutually exclusive ones.
In practice
Modifiers are the "large", the "no onions", the "extra cheese" and the "half and half". They are the part of a menu that decides whether a till or an ordering system is pleasant or infuriating, because they are where every real menu stops being a simple list.
A good model handles three things: options that cost nothing, options that cost money, and options that are mutually exclusive. It also handles the awkward cases — a choice that changes the price of the meal deal rather than the item, or an option only available on one size.
Where a system cannot express a modifier, staff work around it with notes, and notes do not appear in reports or stock. That is how a shop ends up unable to say how many large ones it sold.
Also called: item options, menu options.