Reciprocity (international Relations) , a principle that favours, benefits, or penalties that are granted by one state to the citizens or legal entities of another, should be returned in kind.
Ethic Of Reciprocity , a general philosophical principle, the most common formulation is known as The Golden Rule -- "Do unto others as you would have others do unto you".
SEE ALSO
Symbiosis , an interaction between two organisms living together in more or less intimate association.