What is meant by Nofollow links?
Nofollow links are links to a rel = "nofollow" HTML tag applied to them. The nofollow tag tells search engines to ignore that link. Because nofollow links do not pass PageRank, they are unlikely to affect search engine rankings.
Nofollow vs Dofollow Links - What's the Difference?
The only technical difference between the two is that a nofollow link has a nofollow tag.
Before nofollow was used for individual links, quite a lot of work was required to prevent robots from following links on a page (for example, you could redirect the link to a URL that was blocked in robots.txt). This is why the nofollow attribute value for the rel attribute was created. This gives webmasters more detail control: instead of prompting search engines and crawlers not to follow any links at all on the page, it is now easy to point out a particular link that should not be followed. Example:
As a user, it is impossible to tell the difference between a nofollow and a dofollow link. You can click, copy and use a nofollow link like any other link on the web.
But when it comes to search engine optimization there is a big difference between nofollow and dofollow links.
The difference is this: Dofollow links help your search engine rankings. Nofollow links do not.