Reciprocal link
A reciprocal link is made by placing a link somewhere on your website and in exchange the owner of that website will link back to you. Reciprocal linking between websites can be important of the search engine optimization process because Google uses link popularity algorithms (defined as the number of links that lead to a particular page and the anchor text of the link) to rank websites for relevancy.
Google Do
The best way to get other sites to create relevant links to yours is to create unique, relevant content that can quickly gain popularity in the Internet community.
Why does Google care about Reciprocal linking
Your site's ranking in Google search results is partly based on analysis of those sites that link to you. The quantity, quality, and relevance of links count towards your rating. The sites that link to you can provide context about the subject matter of your site, and can indicate its quality and popularity. However, some webmasters engage in link exchange schemes and build partner pages exclusively for the sake of cross-linking, disregarding the quality of the links, the sources, and the long-term impact it will have on their sites. This is in violation of Google's Webmaster Guidelines and can negatively impact your site's ranking in search results.
It is not only the number of links you have pointing to your site that matters, but also the quality and relevance of those links.