小区 (xiǎo qū) refers to a specific residential community or housing estate, often gated, with multiple buildings and shared facilities. It's more concrete than 附近 (fù jìn, 'nearby area') or 区域 (qū yù, 'region'), and unlike 社区 (shè qū, which emphasizes the social community), 小区 is a physical, bounded place. 城区 (chéng qū) is a much larger urban district, not a single housing development.