Reciprocal is a link building strategy employed to exchange links between two websites  to ensure mutual traffic. For instance the strategy would work this way, Adam and Eve own websites. If Eve’s website adds a link to Adam’s website, and Adam’s website also adds links to Eve’s website, the websites are reciprocally linked.

Reciprocal link building strategy works best between websites that have relevant content or have niche content and traffic related to the same. In a case where a website that has content and traffic relevant to the target of the link, it results in a high PR link that is built.

Such Link Building Strategies work good, because Google uses link popularity algorithms (defined as the number of links that led to a particular page and the anchor text of the link) to rank websites for relevancy.