Expiation (noun)
– the act of making an atonement
– make amends or reparations for

Taken from Chimamanda Ngozi Adichie’s “You In America”

“You wanted to write about the way people left so much food on their plates and crumpled a few dollar bills down, as though it was an offering, expiation for the wasted food.”

After finding a job at a local restaurant, the protagonist wanted to send letter to her family about her experiences at work and such, one instances is the text above. Expiation on this context meant to show that some customers leave a couples bucks in order feel better about themselves for wasting so much food. Knowing the definition of the word “expiation”, I’ve learned that the customer’s thought process about their wasteful action is that it will somewhat clear their conscience.

source:
https://www.merriam-webster.com/dictionary/expiation
http://www.dictionary.com/browse/expiate