Call Parking is the modern term for placing calls on hold that can easily be picked up on a different phone.
If your phone system has Call Parking enabled, you will likely see some buttons on your phone labeled "Hold X" or "Park X" where X is a number, usually from 1 to 4.
These buttons will be either Green or Red, depending on if there is a call parked on that line or not.
Green means the Call Park line is available.
Red means the Call Park line is currently in use by someone on hold.
When you are currently speaking with someone, find a green Park Line, then press it - The call will disappear from your phone, and the Park Line will now turn red.