When two or more people or nations have equal exchanges of goods or services, they are enjoying reciprocity, a situation where each enjoys an equal benefit from the relationship.
The background of the word reciprocity can be traced to the Latin reciprocus which means, logically enough, "moving back and forth." This is an appropriate meaning for a word that describes a system that moves goods and favors back and forth between participants, sort of a business version of the Golden Rule or, in a different light, the expression "you scratch my back and I'll scratch yours."
