I think our 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 influences your ranking. The sites that link to you can provide context about the subject matter of your site, and can indicate its quality and popularity.
Any links intended to manipulate a site's ranking in Google search results may be considered part of a link scheme. This includes any behavior that manipulates links to your site, or outgoing links from your site.