The Collaborative International Dictionary of English v.0.48:

Barrio \Bar"ri*o\, n.; pl. Barrios. [Sp.]
   In Spain and countries colonized by Spain, a village, ward,
   or district outside a town or city to whose jurisdiction it
   belongs; in Spanish-speaking areas of cities in the United
   States, it is a neighborhood, ward, or quarter inside a town.
   [Webster 1913 Suppl. +PJC]

WordNet (r) 3.0 (2006):

barrio
    n 1: a Spanish-speaking quarter in a town or city (especially in
         the United States)
    2: an urban area in a Spanish-speaking country

Moby Thesaurus II by Grady Ward, 1.0:

34 Moby Thesaurus words for "barrio":
   Bowery, Chinatown, East End, East Side, Little Hungary,
   Little Italy, West End, West Side, black ghetto, blighted area,
   business district, central city, city center, core, downtown,
   ghetto, greenbelt, inner city, midtown, outskirts,
   red-light district, residential district, run-down neighborhood,
   shopping center, skid road, skid row, slum, slums, suburbia,
   suburbs, tenderloin, tenement district, uptown, urban blight