What racial concept did the oldest v. Ferguson decision uphold?

The Plessy v. Ferguson decision upheld the racial concept of "separate but equal." This legal doctrine maintained that racial segregation was constitutional as long as the separate facilities for African Americans and whites were deemed equal in quality. This ruling effectively legitimized state-sponsored racial discrimination and segregation, reinforcing systemic racism in the United States until it was overturned by Brown v. Board of Education in 1954.