Of African native descent.
It gets a little blurry when dealing with North African Arabs or what fraction of descent is required to be considered black.
Do you believe there is a cultural definition of "blackness"?
Yes, there is a cultural understanding of "blackness" as a cultural identity and set of customs. But, it is still a term regarding ethnicity, much like there is a cultural understanding of "Irish-Americanness" or "Italian-Americanness". Those definitions are also first and foremost ethnic terms. No matter what cultural behaviors I adopt I will never be black or an Italian-American.
Huh? "Blackness" is nothing but a stupid and ignorant stereotype.