1. <communications> The exchange of call control information
on a dedicated channel, separate from that used by the
telephone call or data transmission.
2. Sometimes used to describe what communications people call
"shift characters", such as the ESC that leads control
sequences for many terminals, or the level shift indicators in
the old 5-bit Baudot codes.
3. In personal communication, using methods other than
electronic mail, such as telephone or snail-mail.
4. <software> Values returned by a function that are not in
its "natural" range of return values, but rather signal some
kind of exception. Many C functions that normally return
a non-negative integer return -1 to indicate failure.
This use confuses "out-of-band" with "out-of-range". It is
actually a clear example of in-band signalling since it uses
the same "channel" for control and data.
