White is a racial classification and skin color specifier, generally used for people of European origin; although the definition can vary depending on context, nationality, and point of view. This term has at times been expanded to encompass persons of South Asian, West Asian, and North African descent, persons who are often considered "non-white" in other contexts in the United States. It has also been alleged that, in the United States, people of Southern European and even Irish descent have been excluded from this category, although this idea has been contested. 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 physical characteristics, and contrasting with "black", "red", "brown", "yellow", and other "colored" people or "persons of color", originated in the 17th century. Prior to this, Europeans also described people from East Asia as being "white". It was only during the 19th century that this vague category was transformed in a pseudo-scientific system of race and skin color relations.