Toxic Backlinks

What are toxic backlinks? Google states it like this:

HARefs has a simplified explanation of link quality:

What Makes a Backlink Toxic?

There are several things which can increase the toxicity of a backlink from a search engines perspective including:

Low domain trust score - This is based on the number of backlinks from trusted domains to the domain providing the backlink. A low rank means the site’s domain score may be artificially inflated. 

Mirrored pages – If similar pages on multiple sites are linking to you from the same anchor text, search engines may see this is a link building scheme.