Mean Attribute Nofollow In Link

nofollow is a value that can be assigned to the rel attribute of an HTML a element to instruct some search engines that a hyperlink should not influence the link target's ranking in the search engine's index. It is intended to reduce
the effectiveness of certain types of internet advertising because their search algorithm depends heavily on the number of links to a website when determining which websites should be listed in what order in their search results for any given term.

The nofollow value was originally suggested to stop comment spam in blogs. Believing that comment spam affected the entire blogging community, in early 2005 Google's Matt Cutts and Blogger's Jason Shellen proposed the value to address the problem.
The specification for nofollow is copyrighted 2005–07 by the authors and subject to a royalty free patent policy, e.g. per the W3C Patent Policy 20040205, and IETF RFC 3667 & RFC 3668. The authors intend to submit this specification to a standards body with a liberal copyright/licensing policy such as the GMPG, IETF, and/or W3C

Just because they don’t provide SEO link value doesn’t mean no follow links are worthless. No follow links still provide valuable referral traffic.
A well-placed blog comment or a relevant forum post, no follow or not, can send a huge amount of traffic to your site, which then can funnel down to leads and conversions!
Besides, search engines today are looking at a lot of factors outside of link juice and PageRank. Social signals like those from Twitter and Facebook are increasingly valuable, despite being no follow. The key is to build your brand – don’t think of what links are good for SEO, but instead think what links are good for your business, your brand, and what links can help establish you as an industry authority. Remember that links, no follow or not, build trust.