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The one-drop rule is a legal principle of racial classification that was prominent in the 20th-century United States. It asserted that any person with even one ancestor of black ancestry ("one drop" of "black blood") is considered black (Negro or colored in historical terms). It is an example of hypodescent, the automatic assignment of children of a mixed union between different socioeconomic or ethnic groups to the group with the lower status, regardless of proportion of ancestry in different groups.