A shortened version for "fat upper crotch area". Fuca is usually used as a plural form of a group with both genders. Fuca may also be used for a single person, if they are confused as to what gender the fuca is.
Renata: Man look at that guy over there...he definitely could lose a few pounds.
Alexsandra: Really? Cause I think his fuca looks damn sexy. Imagine trying to actually find a penis in that...Mission Impossible 5.