outside of smart things, “Orphan” is from the child’s point of view
In network engineering, an “orphan” device is one that has lost contact with its “parent.”
The technical details are different for different protocols: sometimes it is used to mean a battery-powered device that has lost contact with a repeater, but still knows who the network Coordinator is.
Other times it means a device that tries to join a network and fails, so has no recorded parent.
And still other times it means a device that now needs to be moved from one network to another, so it has a recorded parent but you want to use a different one.
But these three situations are always from the end device’s point of view. The child device has a listed parent that it cannot find, or has no parent listed at all.
outside of smartthings, “ghost” and “zombie” are from the network controller’s point of view
In contrast, the term “ghost device” is from the controller’s point of view. it means that there is a device in the controller’s device table that is not actually connected to the network.
Sometimes a ghost is a duplicate that was created during a failed pairing. Sometimes it’s an entry that did not clear during a failed removal. Either of these is more likely to happen in a cloud architecture because there are actually multiple copies of the network device table, usually one in the hub and one or more in the cloud. It can also be caused by database corruption, when a device from one account shows up in the cloud’s device listing for another account.
A “zombie” device is a ghost that keeps coming back even though you have removed it multiple times. This is almost always a synchronization problem and means that you removed it from one table but then it got restored again from another.
But SmartThings uses its own terminology
As with several other terms, SmartThings tends to make up its own definitions to avoid having to distinguish between different protocols.
So SmartThings support staff, and consequently many community members, Will use the term “orphan” for what is more typically called “ghost” and don’t use the term orphan the way it is most typically used.
So a zigbee device which fails to secure a network ID during pairing is not called an orphan in SmartThings. It’s just called a failed pairing.
But ghosts and zombies, that is, devices which have entries in the device table even though they are not actually joined to the SmartThings network, are called “orphans” in SmartThings support terminology. (Even though in this case it’s the parent that can’t find a listed child, not the child missing a listed parent.)
SmartThings also introduced the term “child device” for a programming construct and then describes those as “orphaned devices” for situations where only the handlers were changed, not the device pairings themselves. It even uses the term “child device” for web services situations where there was no pairing at all.
This can all make it pretty confusing if you try to look up the term in general resources. Especially since the solutions for ghosts and orphans are different. But there it is. (Smartthings also says zwave devices have “clusters,” which they don’t- – that’s a zigbee term.)
short answer: SmartThings uses “orphan” when there is a synchronization problem with the network address tables
But is not very consistent about how the term is used, and does not use it in the way that it is generally used in network engineering.
In the following thread, for example, a community member gives a helpful explanation of how to remove a zwave ghost device from the network device table – – but calls it an “orphan” because that’s what SmartThings support calls it. 