Reciprocity is a concept in social psychology and sociology that refers to the principle of mutual exchange or give-and-take between individuals or groups. It is the idea that people are more likely to help those who have helped them in the past or to return a favor that has been done for them. Reciprocity plays a key role in shaping social relationships, influencing behaviors such as cooperation, trust, and altruism. Researchers study reciprocity to understand how it influences social interactions, cooperation, and the maintenance of social norms and relationships.