What does the medical abbreviation W and D mean?

"w/" commonly means with; "w/o" means without. In medicine, "w" may mean weight or width. In chemistry, "W" is the symbol for Tungsten.

"D." or "d." commonly mean day or date. In medicine, "D." or "d." may mean dose. In chemistry, "D" is the symbol for Deuterium (an isotope of Hydrogen).

Without context, it's difficult to be sure, but it's most likely either "with" or "weight" and "dose"

"WD" can mean well developed and is written on many physical exam reports in the section describing the general appearance of the patient.