Those aspects of society that overtly and covertly attribute value and normality to white people and Whiteness, and devalue, stereotype, and label people of color as "other", different, less than, or render them invisible. Examples of these norms include defining white skin tones as nude or flesh colored, having a future time orientation, emphasizing individualism as opposed to a more collective ideology, defining one form of English as standard, and identifying only Whites as great writers or composers.
I understand why Volokh would be upset: being a libertarian, he probably would identify as an individualist, and does not like that being equated to "racist." As for Critical-Race-Theory-Hack me, I think this definition oversteps itself.
The last stop on my intellectual voyage prior to landing on Critical Race Theory was non-interventionist liberalism that was slowly spiraling into libertarianism. I didn't actually like libertarianism that much, and was glad to be rescued from what had seemed logically infallible but morally intolerable. However, this doesn't mean I condemn individualism. On the contrary, enough John Stuart Mill runs in my veins that I'd be very hard pressed to express hostility toward individualism on the whole. What Critical Race Theory taught me was that an individualist paradigm cannot "see" all forms of racism. So remaining excessively committed to individualism means consenting to the preservation of racial hierarchy.
But one can concede that and still "emphasize" (Seattle's words) individualism over collective ideologies. Collectivist mentalities, after all, can miss racism too--an "all for the corporation" mentality might explain the firing of a Black worker on the grounds that his productivity was sub-par, not noticing that he had a racist manager who was constantly harassing him (even while putting in great work of his own). Or a viewpoint that examines racism solely through groups can overlook individual acts of prejudice that fall outside "normal" structures, institutions, or cultural memes, but still exert significant negative impacts on their targets.
Within this paradigm, people will disagree about where the line should be drawn between collective and individualist ideologies. But merely deciding to "emphasize" individualism is not so clearly beyond the bounds as to be unquestionably deserving of the tag "racism."
Volokh also registers at least a theoretical opposition to Seattle's claim that listing only Whites as the greatest composers or writers is racist. This seems a bit tougher to defend. There is no objective way of determining who the "best" writer is. And I have a lot of trouble conceptualizing a criteria choice that a) excludes all minorities, b) has no racial component at least implicit, and c) falls within a sensible definition of the term "greatest." For example, saying "the greatest writers are those with the greatest impact on the world," and including only Whites, seems difficult to justify without denying the historical, political, and cultural importance of the non-Western world. I suppose stretching to the limits of abstractness, I can imagine a list that includes only Whites that has no racial element to it whatsoever. But pragmatically, I'd ascribe only a minimal probability to that being the case for any given list that excluded all minorities, and my default assumption would be that any such list is tainted by some manifestation of racial hierarchy..