What term describes overcrowded buildings where many immigrants lived in the U.S.?

The term that describes overcrowded buildings where many immigrants lived in the U.S. is "tenements." In the late 19th and early 20th centuries, particularly during the waves of immigration to America, many immigrants settled in urban areas and often found themselves living in these poorly constructed and densely populated apartment buildings known as tenements.

Tenements were typically designed to maximize rental income and often lacked adequate sanitation, ventilation, and safety measures, leading to very poor living conditions. These living environments were a reflection of the social and economic challenges faced by immigrant populations at that time, highlighting issues of housing accessibility and urban poverty.

In contrast, houses generally refer to single-family dwellings, condos are modern forms of housing ownership that usually come with amenities, and barracks are military-style housing. None of these alternatives capture the specific context and conditions associated with the overcrowded immigrant living situations of the era. Thus, "tenements" is the appropriate term for these overcrowded, often substandard buildings where many immigrants made their homes.