And yet, there it was in the recent Supreme Court decision on affirmative action. The plaintiff, noted Justice Anthony M. Kennedy in his majority opinion, was Caucasian. 

To me, having covered the South for many years, the term seems like one of those polite euphemisms that hides more than it reveals. There is no legal reason to use it. It rarely appears in federal statutes, and the Census Bureau has never put a checkbox by the word Caucasian. (White is an option.) 

The Supreme Court, which can be more colloquial, has used the term in only 64 cases, including a pair from the 1920s that reveal its limitations. In one, the court ruled that a Japanese man could not become a citizen because, although he may have been light-skinned, he was not Caucasian. In the other, an Indian was told that he could not become a citizen because, although he may have been technically Caucasian, he was certainly not white. (A similar debate erupted more recently when the Tsarnaev brothers, believed to be responsible for the Boston Marathon bombing, were revealed to be Muslims from the Caucasus.) 

The use of Caucasian to mean white was popularized in the late 18th century by Johann Friedrich Blumenbach, a German anthropologist, who decreed that it encompassed Europeans and the inhabitants of a region reaching from the Obi River in Russia to the Ganges to the Caspian Sea, plus northern Africans. He chose it because the Caucasus was home to “the most beautiful race of men, I mean the Georgians,” and because among his collection of 245 human skulls, the Georgian one was his favorite wrote Nell Irvin Painter, a historian who explored the term’s origins in her book “The History of White People.” 

 In 1889, the editors of the original Oxford English Dictionary noted that the term Caucasian had been “practically discarded.” But they spoke too soon. Blumenbach’s authority had given the word a pseudoscientific sheen that preserved its appeal. Even now, the word gives discussions of race a weird technocratic gravitas, as when the police insist that you step out of your “vehicle” instead of your car. 

“If you want to show that you’re being dispassionate then you use the more scientific term Caucasian,” Ms. Painter said. 

Susan Glisson, who as the executive director of the William Winter Institute for Racial Reconciliation in Oxford, Miss., regularly witnesses Southerners sorting through their racial vocabulary, said she rarely hears “Caucasian.” “Most of the folks who work in this field know that it’s a completely ridiculous term to assign to whites,” she said. “I think it’s a term of last resort for people who are really uncomfortable talking about race. They use the term that’s going to make them be as distant from it as possible.” 

There is another reason to use it, said Jennifer L. Hochschild, a professor of government and African-American studies at Harvard. “The court, or some clever clerk, doesn’t really want to use the word white in part because roughly half of Hispanics consider themselves white.” She added, “White turns out to be a much more ambiguous term now than we used to think it was.” 

There are a number of terms that refer to various degrees of blackness, both current and out of favor: African-American, mulatto, Negro, colored, octaroon. There are not a lot of options for whites. In Texas, they say Anglo. And there is the pejorative we were so pithily reminded of when a witness in the racially charged George Zimmerman trial said the victim, Trayvon Martin, had called Mr. Zimmerman a “creepy-ass cracker.” 

IN the South, I was often asked about my ethnic origins, and I had a ready answer. “My father is from India,” I would recite, phrasing it in such a way as to avoid being mistaken for an American Indian. “And my mom is white.” Almost invariably, if I was speaking to black people, they would nod with understanding. If I was speaking to white people, I would get a puzzled look. “What kind of white?” they would ask. Only when I explained the Norwegian, Scottish and German mix of my ancestry would I get the nod. 

I theorized that this was because blacks understood “white” as a category, both historical and contemporary — a coherent group that wielded power and excluded others. Whites, I believed, were less comfortable with that notion.
But Matthew Pratt Guterl, the author of “The Color of Race in America, 1900-1940,” had a different take. “They’re trying to trace your genealogy and figure out what your qualities are,” he said. “They’re looking in your face, they’re looking in the slope of your nose, the shape of your brow. There’s an effort to discern the truth of the matter, because all whitenesses are not equal.” In other words, they weren’t rejecting the category, they were policing its boundaries. 

Such racial boundaries have increasingly been called into question in the debate over affirmative action, once regarded as a form of restitution to descendants of slaves, but now complicated by all sorts of questions about who, exactly, is being helped. “What if some of them aren’t poor, what if some of them don’t have American parentage, what if some of them are really stupid?” Ms. Painter, the historian, asked. “There’s all kinds of characteristics that we stuff into race without looking, and then they pop out and we think, ‘I can’t deal with that.’ ” 

Doubtless, this society will continue to classify people by race for some time to come. And as we lumber toward justice, some of those classifications remain useful, even separate from other factors like economic class. Caucasian, though? Not so much. 

Shaila Dewan is an economics reporter for The New York Times.