A no follow link is one that does not pass any link juice or SEO value to the target URL. This type of link is usually used when linking out to websites that are not trusted or are irrelevant to the content of the page that it appears on.
No-follow links can also be used as a way to reduce spam from users who link from their comments or forum posts. No-follow links can still be beneficial for driving traffic to your website, but will not have a positive impact on your own website’s search engine rankings.