= O =
[from telecommunications and network
theory] 1. In software, describes values of a function which are
not in its `natural' range of return values, but are rather
signals that some kind of exception has occurred. Many C
functions, for example, return a nonnegative integral value, but
indicate failure with an out-of-band return value of -1.
Compare hidden flag, green bytes, fence. 2. Also
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 email, such as telephones or snail-mail.
--The Jargon File version 4.3.1, ed. ESR, autonoded by rescdsk.