a girl whose medium size. Not fat nor skinny, Just average. A Thick girl usually haves a curvy/slim waist with a big behind, hips AND thighs.
Beyonce, Ashanti, and Ciara are examples of being thick cuz they're not fat or skinny, They have a hourglass figure. Small Upper Body,(arms, waist, etc), Thick Lower Body (big booty/ hips/thighs/big calves or shapely nice legs)