Spam Rating is a score created by Cocolyze which allows us to analyse the toxicity risk of a link. The Spam Rating is a mark, between 1-10, 10 being of high toxicity risk.
We consider a potentially toxic link a link that could badly influence the quality of a website's netlinking, and therefore its Google ranking. A toxic link for example can be a link from a poor quality website, such as an online casino in a foreign country with an uncertain reliability which points a link towards your site, even though you have no connection with the casino world. Google could penalize your ranking if there is a high number of poor quality sites linked to yours.
The Spam Rating score doesn't indicate the toxic links but the links that have a high toxicity risk. We advise that you manually check the links with a Spam Rating superior or equal to 8: if you think that some of these links aren't linked to your activity and are suspciously unreliable, you can disavow these links with Google to tell them that you don't want Google to take them into account.
Here is an article from Google explaining how to disavow your backlinks.
The Spam Rating is calculated by powerful algorithms from our own research and development. In simple terms, this score rests on popularity, confidence of the referring site, its quality and the analysis of the present links on the page. A website with a high popularity level (i.e. with lots of links) but poor quality (i.e. a weak confidence score) will be considered as potentially toxic.