out-of-band

adjective4

1. •
   Taking place outside of a defined telecommunications frequency band.
2. •
   Transmitted on a different channel, or by a different method, from that of the primary communication channel.
3. •
   Relating to communication, such as identity verification, via a method other than the primary means of accessing the software.

   • One great way of solving the phishing problem is doing out-of-band authentication. — 2007
4. •
   Of a value returned by a function: not in its natural range of return values, but rather signaling an exception.