What Are Variables? — Definition & Examples

A group of mathematicians have conspired together to write the most frustrating cookbook to ever exist. All of the amounts are listed in variables, in order increasing with size of the ingredient ($a, b, c, d, e$, and so on). If a recipe involved a tablespoon of sugar, a pinch of salt, a whole turkey, and one full onion in that order, what series of variables would represent it?