In the U.S., a barrio is the neighborhood where most people speak Spanish. For example, in New York, Spanish Harlem is also called El Barrio. Outside the U.S., barrio refers to a district in Spain or a Spanish-speaking country.
The word barrio means "neighborhood" in Spanish, and in most Spanish-speaking places, that's exactly what it means. In Cuba and Spain, barrios are official divisions of municipalities. But in New York, Los Angeles, Tucson, Miami, and other U.S. cities, a barrio isn’t an official district, it’s just the neighborhood where Spanish speakers settled and/or still live.