Woman's mental disorder - excessive interest in and indulgence in sex. When a man has a similar disorder, it's satyromania. An authority on it should know a lot about it. But, depending on the context, 'authority on nymphomania' may have been used rather 'more loosely' (which is a charitable way of saying 'inaccurately'

) to mean
sex-mad (in a possibly non-pathological sense).
b