The word “epistemology” refers to the study of knowledge and its formation, so an epistemology of ignorance would involve creating “knowledge” based on . . . a profound lack of knowledge or stupidity. Using fancy academic language, Mills is basically saying that whites’ ideas “about race” are fundamentally based on misrepresentations and distortions of social reality, but their “not knowing,” their ignorance, gets routinely repackaged as credible, authoritative “knowledge,” even as “science.”