Might it be something to do with Fanny Phelps, the occupant, being a Midwife - e.g. Maternity ….
I can only think of ‘Maternity Department’ but it seems to have been a private house.
If it follows the address, you would think it is relevant to the address, rather than a person.
The previously linked article mentions her being there in 1925 and the Midwives roll shows her there in 1931.
Could it be a badly written ‘U’ for Urban District, if it follows the word ‘Bemerton’.