Editorial references
A writer may link because a resource supports an argument, provides evidence or helps the reader take another step. The acquisition method and editorial context matter. A link in a useful industry article is different from an unrelated reference added without a clear reason.
Sponsored and user-generated links
Google recommends rel="sponsored" for advertisements or paid placements, and rel="ugc" for links in user-generated content such as comments and forum posts. These attributes describe the relationship; they are not labels for a particular page design. A sponsored link may appear in an article, not just a banner.
Followed links and nofollow
People often use “dofollow” to describe an ordinary link without a restrictive rel attribute. It is not a special HTML attribute that must be added. Nofollow is another relationship value used when the other values do not fit and a site does not want to imply endorsement. Check the actual markup rather than a sales label.
Classify the same link in more than one way
A record can describe placement type, acquisition route and HTML attributes separately. For example, a guest article is a content format; whether it is sponsored depends on the arrangement, and its rel attribute is a separate technical detail. Keeping these fields separate makes comparisons and reports less misleading.