This is defined as a side chick who has few morals and who let's you have sex with her even when you may already have a wife/girlfriend. The girlfriend/wife is the meal. The side chick is just a "snack".
Kyle: “did you see Jenny at the party last night? The way she was shaking that ass really turned me on!”
Jessie: “the hosnack? I saw her but she was busy flirting with Steve and Jeremy so I didn’t have the chance to ask if she might be into women too.”