rel="nofollow" attribute value on a link element specifies that the link is not endorsed and is not controlled by the current website.
rel="nofollow" on an <a> tag.
This link is not endorsed or controlled by the current site.
Go to <a rel="nofollow" href="https://apple.com" target="_blank">Apple</a>
The rel attribute defines the relationship between the current page and the linked page or resource.
rel="nofollow" value instructs search engines not to follow the outbound link.
Effectively, the current site does not want the linked page to be associated with the current site.
<tagname rel="nofollow" href="url" />
These elements accept the nofollow value on the rel attribute.
|<a>||Specifies an anchor link -- see example above|
|<area>||Creates clickable areas inside an image map.|
|<form>||Specifies an HTML form.|
rel="nofollow" value was added with the introduction of HMTL5.
In 2019 two alternative rel values were announced: sponsored and ugc (user generated content).
rel="sponsored" value indicates paid links or links that the site owner is compensated for.
rel="ugc" value indicates forum posts or comments that are created by the users.
These alternatives to "nofollow" offer developers more ways to identify their links to search engines.
Here is when rel support started for each browser: