On most VoIP systems, “hold” is essentially keeping a conversation (set of channels) connected, with the microphone and speaker off. It allows you to make another call, etc., but is specific to the phone and conversation.
On many phones there is a hold button, or a way to put a call on hold through the menu.
Hold uses a “line” on a phone, and holds it there.
You cannot share a line on hold, but you might or might not be able to transfer it, depending on the phone being used.

“Parking” allows you to put a call on hold in a manner that can be picked up by another phone.
This is essentially putting it on hold at the phone system/PBX/Hello Hub, so that others can pick it up.
When you park a call, it goes into a parking lot slot.
Hello Hubs have 9 slots, 601,602,603…609 for parking calls.
We try to configure phones to emulate a 1950's phone key system where you park a call, and it can be retrieved by others.

If your handset has a button for Park 600, then simply press it to park the current call.

If your phone does not have a Park button, you can do it the old-fashioned way:

• Transfer the call to extension 600
• Listen for the announcement that says the extension number where the call is parked.
  • Calls are assigned to the first available extension starting with 601, moving to 602, 603… 609.
• To retrieve the call from the same or any other phone on the network, simply dial the extension announced to you in the previous step.