What, exactly, IS "race" (or is it just race)?

If we're going to define racism, it strikes me that the next step is to define race, especially if, ultimately, what we want to do is to come up with strategies for an anti-racist praxis.

My own definition of race was influenced while I was in college by Michael Omi & Howard Winat's Racial Formation in the United States (it's going into a 3rd, post 9/11 edition). [I'm withholding my own definition entirely, this time, to hear what others have to say, although if you've read Omi & Winant you can figure out how I define race pretty easily].

So once again, I throw out this question to the blogosphere: How do you define race? Does it differ depending on context/audience? And especially for those of you in the classroom who talk about, teach about, issues of race/diversity/ethnicity/culture, how do you define race for your/with your students? What are their points of resistance/acceptance? And what strategies have you found that work best to talk about race (and racism and anti-racism)?