What's the Meaning of Black Blood Backgrond?

Oaso: The first thing to understand about this, right, is, like, oaso the the the initial, the very, very beginning of the cultured revolution. And these kids are kids who have what's called a black blood background, like black blood, which means that they're the children of people from bad class backgrounds. They weren't allowed to hold any government position because their dad had made bird feeders before the revolution and was considered petite bourgeois.