Indirect backlinks refer to backlinks that point to a page that links to the site that an SEO professional is attempting to rank. Search engine ranking algorithms have evolved to understand webs of important sites, and it's an extreme understatement that not all backlinks are created equal.

For this reason, it grows harder and harder for those practicing black hat SEO to spam large amounts of low quality backlinks. It's important now that any backlink of value also possess a respectable number of inbound links itself (either internally or externally on the site that it exists on), and potentially further than this, thus proving it's value on the web as a whole.