Since this question/answer often goes with your other 2 ...
SW means "sex worker" which is an all-encompassing term including SP, MA, Stripper, Camgirl, hooker, prostitute, phone-sex operator, etc.
{SW was used in the past to refer to "street walkers" but they are less likely to be talked about here now since they're not as common as they used to be, it seems now}