The Panoptican is an architectural design of a prison, by Foucault. The main components are; the cells,formed in a curved or circular shape, and; the tower, in which a guard sits, watching over the prisoners in the cells. The point is that the prisoners do not know when they are being watched, since they cannot see the guard in the tower due to lighting, but they know that it could be at any time. So they change their behaviour in order not to get into trouble. Similar effects are seen nowadays with cctv cameras everywhere, though this does not stop all illegal behaviour, of course.
Theoretically, this causes a shift in power. The inmates have no control over when they are being watched, so they become passive recipients, or ‘objects’. The one in the tower holds all the power in the arrangement, and he becomes the ‘subject’, since he ios the only one active in the exchange. This combined with the relative solitude of individual cells, should bring about the control of the hordes of prisoners, according to Foucault.