In American slang, a skank is one who is "skanky". Originally associated with a bad smell and/or scummy or dirty surface, it has come to refer to someone who is either or both physically repugnant for their filth and morally or socially repugnant for their behavior and demeanor, most often sexually. Prostitutes are are often associated with the term though in reference to a usually non-whoring person. It is pejorative.
Examples of use include, "She is a skanky ho*" "You skank" "She is such a skank".
Taken from
http://en.wikipedia.org/wiki/Skank
