Extended definition
Attribute on links (rel="nofollow") telling Google NOT to follow the link when distributing authority. Standard for sponsored links, comments, links to sites you don't want to associate with.
Context and application
Since 2019, Google treats nofollow as a “hint”, not a strict directive — it can decide to follow the link anyway if it considers it useful. More precise variants introduced: rel="sponsored" for paid links and rel="ugc" for user-generated content (comments, forum). If you have a blog with comments, automatically mark links as ugc — it’s the current standard, not generic nofollow.
Related terms
Backlink, Anchor text.