Hi Jill. In the 1841 Census it was only necessary for the enumerator to give the name, if any, of the house, or the name of the street, part of the town, village or hamlet in which it stood. From 1851 onwards they were specifically instructed to give the number of the house as well. The Street is Crossgate and end of each individual family in a house is marked with / and the end of a house is marked with //. There are three families living in the house you are interested in. MB does mean Municipal Borough (of Durham) and PB is Parliamentary Borough (of Durham). Stan