Nofollow is a link attribute that tells search engines not to pass authority signals through to the destination URL. It is added to a link as rel="nofollow" in the HTML and was introduced by Google, Yahoo, and Microsoft in 2005 to combat comment spam. Today it has three working uses: untrusted user-generated content (comments, forum posts), paid placements where editorial endorsement is not implied, and any link the publisher does not want to vouch for editorially. Google replaced the binary nofollow signal with a sliding hint in 2019 — the attribute is still respected but treated as one input among many. Two related attributes have since taken specific jobs that used to belong to nofollow: rel="sponsored" for paid links and rel="ugc" for user-generated content. Nofollow remains the right choice when the link is editorial but the publisher genuinely does not endorse the destination.
Glossary entry