An ergosphere is a type of defined region of space surrounding a rotating black hole. The space is rotating with the black hole rotation, in effect, dragged around, with less rotation, the further from the black hole event horizon. This rotation of the space is called frame dragging. The edge of the ergosphere is defined to be the points where the space is moving so fast that an object "standing still" within the rotating space appears to be moving at the speed of light to a distant observer. The object isn't because the space surrounding it is moving along with it.