Racism is the discrimination against people belonging to an ethnic group. It's related to the belief that some ethnic groups are *inferior than others. Physical characteristics, like skin color, are also considered when the subject is racism. In fact, discrimination against black people is present in many countries around the world. In my country, many people think that calling someone "black" is offensive. I disagree. In my opinion, those people are the real racists, since they view the word "black" with a negative meaning.
(Sorry, but your text is a little limited as your focused example implies that racism is only applied to, as you say, black people, whereas, I know many people from various origins who have suffered racism, regardless of colour).