Answer:
law of diminishing marginal utility
Explanation:
According to my research on different economic terms, I can say that based on the information provided within the question the term being mentioned is called the law of diminishing marginal utility. Like mentioned in the question this term states that the marginal utility of a good or service declines as its available supply increases.
I hope this answered your question. If you have any more questions feel free to ask away at Brainly.