One-way link is a term used among webmasters for alink building campaign. It is a hyperlink that points to a website without any reciprocal link ( What is a reciprocal link?); thus the link goes "one-way" in direction.
It is suspected by many industry consultants that this type of link would be considered more natural in the eyes of search engines. One-way links are also called Incoming Links or Inbound Links.
