What is the difference between ‘nofollow’ and ‘dofollow’ link?

[pharmasecure]

What is the difference between ‘nofollow’ and ‘dofollow’ link?

[RH-Calvin]

Do follow and no follow are link attributes and contain instructions for search engine robots. Do follow links are crawled and indexed in search engines whereas no follow links are never crawled and indexed in search engines.

[vinithaeka]

A NoFollow link is the direct opposite of the DoFollow. It is a unique hyperlink which removes any passing on its specific page rank status to other sites. When the NoFollow option is selected, search engine bots aren’t able to search through the links and therefore skip any content. This in effect means that no rise in search engine ranks can be expected.