What were areas in a city called where most poor working class lived in crowed conditions?

Areas in a city where most poor working-class individuals lived in crowded conditions were often referred to as "tenements" or "slums." These neighborhoods were characterized by substandard housing, limited sanitation, and overcrowding, reflecting the economic hardships faced by their residents. Tenements typically housed multiple families in small apartments, leading to challenging living conditions. Such areas were prevalent during the industrialization period in many urban centers.