|Boott Mills boardinghouse and storehouse, now restored and part of Lowell National Historic Park. Lowell, Massachusetts|
Wikimedia Commons contributors, "File:Boott Boardinghouse Store.jpg," Wikimedia Commons, the free media repository, https://commons.wikimedia.org/w/index.php?title=File:Boott_Boardinghouse_Store.jpg&oldid=125693833 (accessed June 1, 2019).
Most city directories listed whether a resident was rooming, boarding, renting, or sometimes owned a home. “Room and board” is not a term one sees often today, other than perhaps in college fees, and most people do not understand the difference between rooming and boarding. When a person rooms, they pay for the use of a bedroom of a private home or boarding house only. They purchase all their meals elsewhere, either at a restaurant or cafeteria.
When a person boards, they not only pay for the use of a bedroom, they also receive meals; the payment to the host is called “room and board.” “Board” refers to the table on which food is served. “Half board” means the boarder receives breakfast and dinner, while “full board” means they receive all three meals as part of their arrangement. This is also where the term “bed and breakfast” came from, in boarding situations where only breakfast was provided. In both rooming and boarding situations, the guest shares the rest of the house with the host and other guests; for instance, the living room or parlor, bathroom, and kitchen and dining areas.
It’s not unusual to see the adult children of your ancestors be listed in city directories as boarders in their own parents’ homes. As these young men and women became of age to start working, typically in their teens, they would find a job and begin to help support the family through their board pay until they were financially ready to set up their own households.
Boarding houses were very common in the nineteenth century, but died out in popularity after the 1930s. Running a boarding house or renting out a room or two was one of the few ways a single woman or widow could earn a respectable living during that time period. Wikipedia has a very good article about the history of boarding houses at https://en.wikipedia.org/wiki/Boarding_house.
In contrast to room and board, when a person rents, they either rent a completely separate residence from the landlord, or they rent a portion of the landlord’s residence and have their own private living, bedroom, bath, and kitchen areas. There is usually a separate entrance to their living areas as well.