What do callouses at the lower base of the pinky toe in the ball of the foot area mean?

Pressure : Callouses develop when there is too much pressure and friction in the area of the foot. You may have biomechanical overload laterally with a tight achilles heel cord. You'll need foot evaluation to receive a clearer picture.

Imbalance: Probably the callus is under the fifth metatarsal head. There are many orthopedic foot conditions that can cause this. I would recommend an evaluation by a podiatrist. Treatment can be conservative with orthotics or possibly surgical.