Reciprocity

noun

1. The characteristic of being reciprocal, e.g. of a relationship between people.

   "In a friendship, reciprocity occurs where the contribution of each party meets the expectations of the other party."

2. A reciprocal relationship.
3. A relation of mutual dependence or action or influence.
4. (grammar) A reciprocal construction involves two noun phrases where each of the participants occupies both the role of agent and patient with respect to the other. see: Wikipedia:Reciprocal pronoun.
5. The mutual exchange of rights, privileges or obligations between nations. see: Wikipedia:Reciprocity (international relations).