Nofollow/Dofollow
Dofollow is the natural default state of all web links that pass Link Equity between pages. Search engines follow these links to find content and share link juice through Internal Links and Backlinks.
Nofollow blocks Link Building value from moving through specific links, though a little may slip through. This exclusion tool works in Robots.txt files, Meta Tags, link attributes, and HTTP headers to control search engine crawling behavior.
Google recognizes three nofollow variations in link tags: standard nofollow for untrusted links, "ugc" for user-generated content like comments, and "sponsored" for paid partnerships. Webmasters pick the right attribute to tell Google exactly what type of link they're dealing with.