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