Racial Discrimination – Acting on prejudices against someone because of their ethnicity/skin colour
Discrimination is treating a person in a worse way than you treat others.
Racial - related to race - divisions of the human species.
Your race is shown on your face and all (racial) humans can be grouped on the basis of these physical characteristics.
So, racial discrimination combines the two meanings above to give:
Racial discrimination: Noticing someone's race and treating them in a worse way than you treat others.