Spam score is an analysis created by Moz based on deep study of Google and the rankings of sites in their massive index. They came up with a list of seventeen factors that, if present on a site, were indicators that the site might be penalized as spam. They call these 17 factors their spam flags.
Moz’s Spam Score is a simple #/17 metric. If your site has 0-4 spam flags, it’s probably fine. If it has 5-7 spam flags, it can be getting into a more troublesome territory. If it has 8-17 spam flags, you’re seriously running the risk of a penalty the next time Google chooses to dole them out.