a synonym for a whore, slut or anyone that cannot keep their legs closed etc. Usually used when referring to a woman, but can also refer to a man. Derived from the American English dictionary word "animal shelter" in that the persons who this word refers to, much like animal shelters, take the "dogs" and (in the male case) "pussies" that no one else wants.
"Wow does that girl sleep with everybody?"
-"yeahhhhhh she's an Animal Shelter..."