A processors package is the part you can see and hold in your hand. It's a substrate with metal pins or pads on the underside and usually a metal heat spreader on the topside. Generally, a single processor die lies under the heat spreader.
Until a few years ago, every processor package contained only one die, and every die contained only one core. Only servers and workstations had two or more processors, which need special motherboards with two or more sockets. If desktop or notebook users wanted better performance, the only way was to buy a processors with higher clockspeed.
Intel and AMD knew that pushing clock speeds into 4GHz area would brought them a lot of technical issues. They should make the processor physically larger, the issue they were avoid of.
The answer was to create dual-core chips with two single-core dies and, later, two cores per die. Quad-core Intel processors debuted in late 2006, and AMD followed with theirs a year after, in late 2007.
The upshot to multicore chips is that in a single processors package, which fits in a single socket on your mother board, you can have up to four CPUs for your desktop PC, notebook, or server.
