alley cat
A derogatory term for a person (typically a woman) considered immoral or promiscuous, especially a prostitute. The term "tomcat" (or "tom cat," literally a male cat) is more common when referring to a man. I'd be wary of her. She's known around here as a bit of an alley cat.
alley cat
A promiscuous woman; also, a person of loose morals. For example, She's constantly picking up men in bars-a real alley cat. This idiom transfers a stray cat that frequents alleys in search of food to a woman of easy virtue, especially a prostitute seeking customers. [Slang; early 1900s]