How does this forum full of young left-wing whites define "blackness"?

[Potus]

Responses are not limited to the young lefty whites.

We had a class discussion about Ferguson that transitioned into a broader conversation about race. There was this sort of assumed definition of blackness held by different classmates. Really, any disagreement was based on a fundamental disagreement on what it means to be black.

[Potus]

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"?