Question

An economic term that describes happiness and is hard to measure in numbers is _____ .

Answer 1

The only abstract answer you pose us with is incentive, which would be most logical to use.

Answer 2

An economic term that describes happiness and is hard to measure in numbers is INCENTIVE.  

In economics, an incentive is what induces a person or agent to act in a certain way, and may be a reward or punishment.

The study of incentives is tremendously important given that they allow explaining or predicting what course of action will take the market or group that affects or applies a particular economic policy. Since rational agents, as long as they are informed about their environment, will compare the costs and benefits of their actions (normally having a strict preference for what benefits them), they will change them in such a way as to maximize their utility.