Discrimination, violent or non-violent, directed against someone of a different race based on the belief that one's own race is inherently superior to all other races.
Just to be clear, there are Black racists, Japanese racists, Chinese racists, Korean racists, and so on and so forth. It is the fallen human nature sadly.
I would go so far as to say that it doesn't necessarily have anything to do with the perceived superiority of one's own race. I would characterize it more as simply
the disliking of another race, for whatever reason. That race could have certain advantages over yours --- more intelligent, more physically attractive, stronger, more talented, more sɛҳuąƖly vigorous, its members more apt to succeed in temporal matters, or what have you --- and you don't like it. It's as old as Cain and Abel. It makes you jealous. It makes you feel threatened because you perceive that the other race could subjugate or otherwise make mincemeat of you, if they took a notion. These are not the things that endear one's race to those of other races who are at a disadvantage compared to your race.
Or it might not even be that complicated. They might just be, pardon me, a pain in the a** --- drive too slowly, drive too fast, hold up the checkout aisle with their complicated grocery purchases, mumble so you can't understand them when they talk, chatter on their cell phones, talk in annoying nasal voices, smell bad (in your judgment), act suspicious, call the police on you at the drop of a hat, any number of things. There are many ways that different social groups can irritate one another.