After gating the clocks of every one of the cores, what other techniques can you use to get even more power savings. Here’s a trivial and admittedly flippant example of what you could do: unplug the processor. You’d be using no power, though the disadvantages of pulling the power plug are pretty obvious. A better idea is to selectively shutdown the more global components of the processor in such a way that you can bring the processor back up to a fully functional state (i.e. C0) relatively quickly.
Package C-States are just that, the progressive shutdown of additional circuitry to get even more savings. Since we have already shutdown the entire package’s circuitry associated with the cores, the remaining circuitry is necessarily common to all the cores, thus the name “package” C-states.