What you are describing is the Module Status column when you have the RSWho browser in spreadsheet mode. The spreadsheet has columns for Address, Device Type, Online Name, and Status.
I'm looking at a 1756 backplane on my test bench right now, and the Status values I see are 'Major Fault' for a controller I know is faulted, 'Idle' for a controller I know has no program in it, 'Self Test' for a DeviceNet scanner that's not connected to a network, and a 1756-ENBT that is alternating between 'Active' and 'Not Keyed'.
When a controller shows 'Unkeyed', that doesn't have a lot of meaning. I think it's just a status code that's shown when there are no other status codes to take precedence.
If the device is an I/O module, the 'Unkeyed' status would actually reflect the Electronic Keying state of the I/O connection.
For this ControlLogix controller, you can safely ignore the 'Unkeyed' state.