Someone who betrays his/her race by siding with another race.
In other words, something that's impossible on Earth since humans are the only setinent race here, and all are 99% genetically identical to each other.
If a male animal and a female animal can under normal circumstances bear offspring, and that offspring is also capable of reproduction, then the male and female animal are same race. Simple biology here, folks.
Amy (a White girl) betrayed Rick (an Asian man) by dumping him for an alien invader from Neptune, while also providing the invaders with aid and support. Thus, she bacame a Race Traitor for betraying humanity.