Stands for The Nerd Theory. That girl in high school who played and dressed the nerd, but is now a SMOKESHOW. In opposition to the "hot" girls in high school, who are now beatsticks.
Jim: "Damn, have you seen Julie recently? She used to be that nerd."
Childish G: "Whatchu know 'bout TNT, Jim. We rockin' for the nerds right now!"