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.
^^^^^
This. Plus one must also self-identify with being black and/or be perceived as black by society. There are a decent number of people out there of African descent whose skin is fair enough that they could potentially be perceived as white. Race is almost entirely a social construct that depends solely on the "rules" of the society you live in. American definitions of race differ wildly from racial definitions in other nations.
Yes, people say that and I agree, but the same people who say that the highest still try to force race outside USA into a American dichotomy, let's take PBS's "Black in Latin America" where Henry Louis Gates jr. try to force a American view of race down over the Dominican and Haitian relationship, and portray the Dominicans as self hating Black people.