It is the notion of ascribing moral, social or political significance to a man's genetic lineage - the notion that a man's intellectual and characterological traits are produced and transmitted by his internal body chemistry.
Racism is a doctrine of, by and for brutes.
It is by his own individual ability and ambition that capitalism judges a man and rewards him accordingly. But capitalism is the only system that functions in a way which rewards rationality and penalizes all forms of irrationality, including racism.