That's a good question.
I'm no expert on the matter, but I will answer to the best of my ability.
Racial trauma can differ from person to person, and it depends on people's experiences. I would say it means being part of a community, institution or group in which you are not included. It's having to navigate that. It might be words that people tell you over and over, it might be experiences you have, it might be discrimination or racism on a daily basis.