It is the rate at which a consumer is willing to substitute one good for another without changing total satisfaction. $MRS_xy = \frac\Delta Y\Delta X$.
The simplest way to understand equilibrium is to look at a consumer who spends his entire income on a single commodity (say, Good X).
The additional satisfaction gained from consuming one extra unit of a commodity ( Consumer Equilibrium Class 11 Notes
[ MU_x = P_x ]
In reality, a consumer buys multiple goods with a limited income. Let us assume the consumer buys two goods, X and Y. It is the rate at which a consumer
(Where ( MU_m ) is the Marginal Utility of money, which is assumed to be constant.)
This assumes satisfaction can be measured in numbers called . The additional satisfaction gained from consuming one extra
The consumer will distribute his income in such a way that the Marginal Utility per rupee spent on every good is equal.