Macrojack:
A macroeconomics term. As explained to me in Economics 101 ... once ice cream is great; two ice creams are very good; five ice creams make you sick. In other words, the more you consume, the lesser the incremental utility (enjoyment) you get for your money.
An audio metaphor might be ... a $400 amplifier (think NAD C320BEE) gets you 85% of the utility/enjoyment that an amplifier would give you. A $2000 amplifier (think Creek Destiny) gets you 95% of the utility/enjoyment. That extra 10% utility would cost you $1600, as opposed to the first 85% would cost you (on average) less than $50 for each 10% utility. That's the law of diminishing returns, in a nutshell.
BTW, most things work this way.
REgards, Rich