Marginal utility (MU) – Additional satisfaction obtained from consuming one additional unit of a good.
Diminishing marginal utility – Principle that as more of a good is consumed, the consumption of additional amounts will yield smaller additions to utility.
MRS = MUX/MUY = PX/PY
Equal marginal principle = Principle that utility is maximized when the consumer has equalized the marginal utility per dollar of expenditure across all goods.