Hi there!
Moz's Spam Score is the percentage of sites with similar features we've found to be penalized or banned by Google (it's not based on the Spam Score of the sites linking to you). Our machine learning model identified 27 common features among the millions of banned or penalized sites in the data we fed it.
Your Spam Score - This does not mean that your site is definitely spammy. The percentage represents a wide variety of potential signals ranging from content concerns to low authority metrics. Since this is based on correlation with penalization, rather than causation, the solution isn't necessarily to change these factors on your site, but it may be worthwhile to consider them. It is best to use this percentage figure to judge the quality of inbound links to your site, giving you a signal to help you determine which of those links needs some further investigation and, perhaps, even removal.
Another site's Spam Score - Again, this doesn't mean that these sites are spammy. This percentage represents a wide variety of potential signals ranging from content concerns to low authority metrics. Since this is just based on correlation with penalization, rather than causation, the solution isn't necessarily to disregard sites or disavow links with higher Spam Scores. Instead, we'd recommend using it as a guide for kick starting investigations. Be sure to check out a site's content and its relevance in linking back to you before disregarding or disavowing.
To improve this score I would recommend reading our guide which explains the 27 factors used to make up this score. You can then look at your site and investigate areas you would like to improve on your site:
https://moz.com/help/link-explorer/link-building/spam-score
I hope this helps!
Jo