At Dictionary.com, there were several definitions for race, including:
- An arbitrary classification of modern humans, sometimes, especially formerly, based on any or a combination of various physical characteristics, as skin color, facial form, or eye shape, and now frequently based on such genetic markers as blood groups.
- A socially constructed category of identification based on physical characteristics, ancestry, historical affiliation, or shared culture: Her parents wanted her to marry within her race.
cde mentions elitism due to blood status, but I want to expand. The first Dictionary.com example definition is interesting in that it identifies blood groups as a basis for an individual to belong to a specific race. In this context, Voldemort's blood purity campaign could qualify as a form of cultural racism. Voldemort wanted pure-bloods to reign supreme and lord over half-bloods and Muggleborns, and he discriminated against them openly. Further, he was willing to kill witches and wizards who were not pure-bloods with impunity.
In Order of the Phoenix, Pansy Parkinson, a white Slytherin girl, taunts Angelina Johnson, a black Gryffindor girl, about Angelina's braided hair. It is common for individuals of African descent to wear their hair in "cornrow" braids, a hairstyle rarely seen in other races. From Order of the Phoenix:
‘Hey, Johnson, what’s with that hairstyle, anyway?’ shrieked Pansy Parkinson from below. ‘Why would anyone want to look like they’ve got worms coming out of their head?’
Angelina swept her long braided hair out of her face and continued calmly, ‘Spread out, then, and let’s see what we can do ...’
Order of the Phoenix - page 261 - Chapter 14, Percy and Padfoot - Bloomsbury
As cornrow braids are very frequently worn by people of African descent -- certainly more so than any other race here in the United States -- Pansy's taunting of Angelina's hair could qualify as Pansy exhibiting racism against Angelina's shared culture, which qualifies as cultural racism, which meets the second definition of racism from Dictionary.com.
Yes, cultural racism is present in Potterverse.
I realize Pansy's taunt does not specifically cite cornrow braids; J.K. Rowling just notes that Angelina has "braids". However, Pansy's specific description of Angelina's braids looking like "worms" would be more consistent with cornrow braids than, say, just two braids, ala Pippi Longstocking. For the record, I do not think cornrow braids look like worms or are unattractive in any way. I am merely talking semantics. Just so that's clear.