A term mexicans or mexican-americans use when they are partying or clubbing and they see a fine skinny girl. They usually scream it out to the beat of the music and point at the girl who they are referring to.
Mexican #1: Hey homes that girl is fine!!
Mexican #2: Yeah bring it back in town. (music playing in the background) La Flaca!!! (screaming while pointing at the girl)
Mexican #1: La Flaca!!!
Mexican:#2: La Flaca!!!