Final answer:
The phrase 'muin - muout = 0' signifies a state of equilibrium in marginal utility, leading to no net change in utility, while 'muin - muout > 0' indicates a beneficial increase in utility.
Step-by-step explanation:
If muin - muout = 0, then the situation describes a state of equilibrium where the marginal utility gained from an economic good or input is equal to the marginal utility lost by taking it away. This implies that there is no net gain in utility, which is the satisfaction or benefit gained from consuming a product or service. On the other hand, if muin - muout > 0, this indicates that the marginal utility from increasing consumption or usage of the good or input is greater than the marginal utility lost. Consequently, there would be an overall increase in utility, suggesting that it would be beneficial to continue increasing consumption or usage of that economic good until the marginal utilities are equalised.