What impact did this case have in America

Even though slavery was abolished in the United States in 1865, racial discrimination did not end with it. States continued to make laws that blocked equal opportunities for African Americans. Homer Plessy decided to test one of those laws to see if he could change it. Plessy lived in Louisiana and, like many people there, he was a Creole; he was not completely white and he was not completely African American. However, in the eyes of the law, he was African American.

I don't get it. What case?