The description of the values of this enumeration is:
Ready: the device can be operated by the user and could even be involved in some operation.
NotReady: the device can not be operated by the user (e.g. due to still being initialized, or due to a device failure,…)
Undefined: it is not possible to retrieve a coherent state from the device (e.g. due to communication, or to contradictory internal states, …)