Audiences are categorized by us into 4 groups: Real followers who demonstrate active and healthy behaviors, as you'd expect from regular accounts. Suspicious/Inactive followers who don't appear to belong to real individuals (for example, accounts lacking biographies, profile pictures, or showing prolonged inactivity). Mass followers who follow more than 1,500 accounts and therefore are not considered typical followers. Influencers, meaning accounts that have more than 2,000 followers themselves, thus also not classified as regular followers.
You can find more information about audience analysis here.