Parking a Call.
On the BLF panel on your phone, you will will see spaces marked SP1, SP2, SP3 and so on. These are shared parking spaces.
If, instead of putting a caller on Hold by pressing the Hold Button, you can press a Shared Parking Button instead. The BLF will immediately turn red to show there is a call parked there. If the call is parked on SP1, for example, then the the BLF on SP1 will be red on every extension on the system. The call can be retrieved from any phone by pressing the the BLF associated with SP1.