A boarding house was a private home where individuals could rent rooms to sleep in.
In 1893, Mrs. Carmichael ran a boarding house. Several time travelling crew members of the USS Enterprise-D stayed there while trying to retrieve Data. Before they left, Jean-Luc Picard mentioned the bill they'd racked up to Samuel Clemens, who offered to settle it for them. (TNG: "Time's Arrow", "Time's Arrow, Part II")