A parked call is a call that is on hold on the phone system instead of a single phone. This allows anyone in the organization to pickup the call.
To park a call, simply perform an attended transfer to extension 70. The system will then announce an extension number. Press transfer again to complete the park. The call can be retrieved by dialing the announced extension number.
Alternatively a call can be parked to a specific slot by performing a blind transfer to extensions 71-74. This allows you to choose the specific parking slot for a call however care must be taken to ensure that a call is not already in the selected slot.