Definition - What does Out-of-Band Management mean?
Techopedia explains Out-of-Band Management
The out-of-band channel management interface is usually available even though the network may be down or even if the device is turned off, in sleep mode, hibernating or otherwise simply inaccessible through the operating system, making this a very powerful management control tool. This can be used to remotely manage powered-down devices outside working hours or during holidays, or it can be used to reboot devices whose operating system has hung or crashed. This is usually done through special operating system extensions and dedicated hardware specifically designed for out-of-band management.
An example configuration for out-of-band management is the use of Microsoft's System Center together with Intel's Active Management Technology and using Microsoft public key infrastructure.