Black People are people of African, Afro-Caribbean, Melanesian, Australian Aboriginal, or Fuegian origin. As none of these people are truly "black" (actually, Europeans aren't really "white"; Asians aren't really "yellow"; and Native Americans certainly aren't "red") this is kind of a redundant term.
In the past, Black people were discriminated against very badly by a whole bunch of dickheads. Thankfully, this is less of a problem today, because of such people as Martin Luther King Jr, Abraham Lincoln, Steve Biko, Nelson Mandela, and William Wilberforce - to name just a few. However, racism is still very common in America; it'd just no longer explicitly written into the law.