type of communication on a communications medium that is sent immediately and directly and isn't held up by any non-out-of-band messages already in the pipeline
adj. Refers to a sentinel or otherwise exceptional value which is distinct from all normal values which can appear in some context (e.g. in a set of function return values, etc.). Compare in-band. Example: EOF (see question 12.1).
In telephony, information carried outside of the audio or voice channel.
Electromagnetic signals are outside the frequency band that the target sends, receives, and processes. An example would be to transmit a 300 MHz signal to damage or upset a communications system that operates in the 500 MHz frequency band.
Transmission taking place external to the allocated bandwidth for this transmission. A video conference with out-of-band audio requires a separate telephone conference call to carry the audio.
Out-of-band is a technical term with different meanings in computer networking, telephony, computer science and operating systems.