Overpronation is one of those terms that is so over abused and misused, especially when it comes to foot orthotics and running shoes. The use of term is more likly to be used by those with a lessor understanding of foot biomechanics, especially runners and those that sell running shoes.
See these references for a better understanding of overpronation:
Overpronation in Runners | Overpronate | Overpronation | Overpronation | Overpronation: Accurate or Parachronistic terminology? | My Advice if you Overpronate | The nonsensical understanding of ‘overpronation’