Basically tells the search engine spiders whether or not to follow a link on your page. The no-follow is typically used on forums and threads to prevent spammers from gaining back-links an adding to their page rank.
I think Do follow link is a hyperlink that can crawled by search engines and which is helpful for increasing the page rank of site while No follow link is a hyperlink that cann't crawled by search engine. No follow link is only used for increasing the visiters.
No Follow Links are the links which does not allows the Search Engine to Visit the site it is linked to.
And Do Follow Links are the links which allows the Search Engine to Visit the site it is linked to
Nofollow is a tag that simply tells search engines not to crawl, or notice, a link on a page.
Dofollow means this link haven't use nofollow tag. Links from DoFollow sites do get noticed by search engines, thus boosting their value
Dofollow Link is a hyperlink that is able to tell all search engines to pass along it’s page rank influence to an outbound link.If you will use or get do follow links then search engines will count your link in the eyes of google, yahoo, bing etc as backlink for your site and you can get some positive value for your site ranking.And other hand nofollow link is exactly the opposite. It is a hyperlink that removes the ability to pass on it’s page rank status to other sites.Nofollow links are for not crawling a link by search engine that influence the ranking of a particular website or blog in search engines.