Backlink

A backlink is a link from a site to another resource located on the Internet. We use backlinks to reference content, just like we refer to books for example.

Links may also mean an endorsement to the linked page, but sometimes you do not want to endorse linked resource, specially for SEO reasons.

HTML attribute rel defines the relationship between linked resource and the current document. From SEO perspective, we use these

  • nofollow
  • ugc
  • external

Nofollow

We use nofollow to indicate that the current document's original author or publisher does not endorse the referenced document. We use this tag in cases, where we want to reference given resource, but don't want to pass "link juice" to it.

Typical use for nofollow backlinks is for links where we don't have control over the referenced content and where links could be exploited for SPAM purposes etc. Example: comments on blogs.

UGC

UGC stands for User Generated Content. Similar as with Nofollow, Google now has specific tag for user generated content that we, webmasters do not have full control and link on our site (for example from comments) doesn't mean owners endorsement.

External

This tag means the resource is outside the site it's linked from - external link. It does not instruct SE to nofollow the link though.