Quite simply, it means "bitch." Its a term often used in areas where people describe themselves, such as online dating sites (which is often the only place for them to get dates, since anyone who encounters them in real life realizes how unpleasant they are.)
Professional women generally have thinly disguised contempt for males, and are likely to remain single and childless well into their 30's, since they are about as nurturing as an electric chair.
I met a chick on Match.com last week who said she was a professional woman. Man, what an angry bitch!
A woman who participates in the workforce and who generally receives some type of specialization or higher education training.
Her mom is a professional woman. She owns her own business and everything!