Caucasian in American usage is becoming obsolete. It once had a legal definition: "of or relating to the White race as defined by law, specif. as composed of persons of European, North African, or southwest Asian ancestry." This from Webster's Collegiate Dictionary.

On police blotters arrests of whites would be marked Caucasian in the blank for race. Real estate contracts often had a restrictive clause- Caucasian race only. This pretty well was abandoned with the rise of the Civil Rights movement and repeal of racial laws. It was used in many restrictive laws and practices.

I don't know if the term is still used in physical and forensic anthropology where it has applications, or whether other, more specific, terms have been adopted.