A girl with a rather large posterior. A "Wide Load".
This comes from Spanglish, as, in actuality, larga means "Long" (not wide or large), but since it is so close to "large" in English, and it rhymes with "carga" (which means "load" in Spanish), it works perfectly in Spanglish.
Bro #1: "Dude, you better be careful! That chick you're talking to is a larga carga!"
Bro #2 (with B.A.C. over .20%): "Not an issue..."
Bro #1: "Bro, I'm surprised she don't have one of them escort vehicles with the flashing lights drivin' behind her!"