The prison industrial complex is the US prison systems being turned over to private businesses from the US Government. The government has cited the lack of funds for our prison system as a partial reason as to why they are operating private, for profit, prisons in the US. It's the US Government's job to administer punishment and operate the institutions in which that punishment is carried out. The 'for-profit' prison system, like every other business in the US, is about private interests of those who operate the prisons. This is not legitimate from any moral standpoint.
I encourage everybody to look into the private prisons in the US and come to your own conclusions.
This isn't something I just so happen to read about. I have been studying this while earning my degree.