The concept of ethnic origin is an attempt to classify people, not according to their current ethnicity, but according to where their ancestors came from. For example somebody living in a monocultural environment, speaking English for example and clearly a member of an English-speaking ethnicity, may be descended from immigrants speaking some other language and still participate in some of their culture and foodways.
Ethnic origin has become a popular classification in statistics, where the concept of race has been largely discarded since World War II, for various reasons. A reaction against the abuses of the Nazis and apartheid made it hard to collect, store or publish racial data. Social scientists in general have lost interest in race as useful concept of study, with many other differences between population groups more significant. However the relative prosperity of distinguishable groups remain of interest in public policy discussions.
In the US, however, the use of the term, race, is still current. The census asks questions about race, though the classification used is no different from what would be termed ethnic origin elsewhere.
