A NoFollow link is a backlink that does not pass link juice. It looks the same as any other link to to the user but to the crawler it says “I don’t vouch for this site so don’t follow this link”.
Google knew that they could not stop using links as votes entirely to determine rankings. Links were (and still are) the best way of determining the quality of a website. But they needed to distinguish between real links created by webmasters and spam links created by SEOs. To do this they created the nofollow tag.
<a href="https://avocadoseo.com/" rel="nofollow">Anchor Text</a>
NoFollow is impressively simple to use, which resulted in it being adopted very quickly. When creating an HTML link a webmaster simply had to insert the tag rel=”nofollow” inside the link and voila – the link was now nearly worthless.
Most forums, guestbooks, wiki websites and other places for user-generated content implemented the NoFollow tag quickly.
There was a noticeable reduction in link spam, but the problem was not eradicated completely. We still see huge amounts of link spam today.
But without the No Follow tag, the web would undoubtedly be a much spammier place.