This term describes an immigrant who traveled to the United States ahead of other family members; this person, often a daughter, found a job, saved as much as possible, and bought a ticket for another family member to come to the United States. This second family member then also got a job, enabling them to bring further family members to the country, repeating the process. The book uses this term to illustrate how poor families were able to immigrate in large numbers.

These factories replaced the segmented manufacturing process that made sweatshops possible and popular. In the garment industry, new-model factories combined all garment-making tasks under one roof, streamlining the process and resulting in hundreds of employees gathered in the same space. These factories are depicted in the book as technological innovations that allowed workers to bond over shared experiences and eventually unionize.

Population density is calculated by dividing the number of people living in an area by the size of that area. For example, a metropolis like Manhattan has a population density of nearly 75,000 people per square mile, an exurban area like Yonkers, New York, has a population density closer to 12,000 people per square mile, and a smaller city located in a rural area, like Albany, New York, has a population density of 600 people per square mile.