White people is a racial classification specifier, used mostly and often exclusively for people of European descent. The term has at times been expanded to encompass certain persons of Middle Eastern, North African, and South Asian descent, persons who are often considered non-white in other contexts. The usage of "white people" or a "white race" for a large group of mainly or exclusively European populations, defined by their light skin, among other characteristics, and contrasting with "black people", Amerindians, and other "colored" people or "persons of color", originated in the 17th century. It was only during the 19th century that this vague category was transformed in a quasi-scientific system of race and skin color relations. The term "Caucasian" is sometimes used as a synonym for "white" in its racial sense and sometimes to refer to a larger racial category that includes white people among other groups.