Answer:
I would say the best definition is A human acting in its own self interest by acting rationally and caring for ones decisions in their own self interest
Explanation:
If you dont like my answer, I beleive this short 5 minutes video will be able to assist you more:
https://study.com/academy/lesson/the-role-of-rational-self-interest-in-economic-analysis.html
Hope This Helped! Good Luck!