1) A horny girl.
2) A dishonest/ lying person; comes from the old southern expression: "You lie like a dog(or bitch) in heat." (Female dogs lie around a lot when in heat)
She's a bitch in heat. (She's a damn liar.)
- The phrase is used as an emphatic tool; it has a kind of harsh connotation, like putting damn in front the word "liar."
The phrase's use is not limited to describing women: "You lie like a bitch in heat son."