Quoting Ancestry, "About U.S. City Directories, 1822-1995":
Whenever you use a directory, it is important to refer to the page showing abbreviations used in the book. Some abbreviations are quite common, such as h for home or r for residence. There may even be a subtle distinction between r for residents who are related to the homeowner and b for boarders who are not related. Becoming familiar with these abbreviations will help you better interpret your ancestor’s listing.