Reciprocity

Reciprocity (or reciprocality) (from the Latin reciprocus, “returning, mutual”; in Russian presumably via the English reciprocity) is the principle of mutual exchange, mutual assistance, or reciprocal interaction. In sociology, it refers to the exchange of gifts and services; in physiology, to the coordinated functioning of neural structures; and in engineering/endodontics, to repetitive back-and-forth motion. Its key feature is that it is based on trust rather than market price.