These are values set for the rel attribute of a href tag (link). They specify the relationship between the web page the link was on and the web page the link is pointing to. There is no effect on SEO, they are used for security and performance reasons.
About the Author: Chad Klingensmith
Chad is a Sr. SEO Strategist for Rio SEO. He has over 10 years of experience in the digital marketing vertical. He enjoys researching and applying cutting edge marketing strategies to help clients achieve optimal online visibility.