One who frequents and/or is an inhabitant of "the street" -- that is, a "skank" who lives, or is often seen, in "public" spaces. The term, which is used, predominantly, to describe a woman or girl, can then, apply to one who is "homeless" and/or (especially) one who is a street-based sex worker.
As a term used to describe (or "name") an individual whose employment is that of street-based sex work, whether that individual is homeless or not, "street skank" is often used in an extremely derogatory manner and, importantly, its denigrating meanings are additional to those implied by "skank": i.e. one who is often considered disgustingly foul, filthy, and sexually "promiscuous".
Some women who perform the service of street-based sex work have however reclaimed the term -- in much the same way as "whore" has been affectionately reclaimed by many sex workers in general.
"She's a street skank"
by Skanky Jane (with a little help from her crew) on Nov 16, 2008