- (telecommunications) relating to activity outside of a defined telecommunications frequency band
2001, Regis J. Bates and Donald W. Gregory, Voice and Data Communications Handbook, page 841:
- In this additional spectrum, in-band signaling was sent down the wires outside the frequencies used for conversation. Actually, the signals were sent across the 3,500- and 3,700-Hz frequencies. Although these worked and were not in the talk path (out of the band) they were limited in the number of tones that could be sent.
- (telecommunications, by extension) relating to communication on a different channel, or by a different method, from that of the primary communication channel
- (computer security) relating to communication, such as identity verification, via a method other than the primary means of accessing the software
2007, Simon Willison, Google Tech Talks: The Implications of OpenID:
- One great way of solving the phishing problem is doing out-of-band authentication.
telecommunications: outside of a defined telecommunications frequency band
telecommunications: on a different channel, or by a different method
computer security: via a method other than the primary means of accessing the software