talk mode: n.

A feature supported by Unix and some other OSes that allows two or more logged-in users to set up a real-time on-line conversation. It combines the immediacy of talking with all the precision (and verbosity) that written language entails. It is difficult to communicate inflection, though conventions have arisen for some of these (see the section on writing style in the Prependices for details).

Talk mode has a special set of jargon words, used to save typing, which are not used orally. Some of these are identical to (and probably derived from) Morse-code jargon used by ham-radio amateurs since the 1920s.

AFAIACas far as I am concerned
AFAIKas far as I know
BCNUbe seeing you
BTWby the way
BYE?are you ready to unlink? (this is the standard way to end a talk-mode conversation; the other person types BYE to confirm, or else continues the conversation)
CULsee you later
ENQ?are you busy? (expects ACK or NAK in return)
FOO?are you there? (often used on unexpected links, meaning also “Sorry if I butted in &ellipsis;” (linker) or “What's up?” (linkee))
FWIWfor what it's worth
FYIfor your information
FYAfor your amusement
GAgo ahead (used when two people have tried to type simultaneously; this cedes the right to type to the other)
GRMBLgrumble (expresses disquiet or disagreement)
HELLOPhello? (an instance of the ‘-P’ convention)
IIRCif I recall correctly
JAMjust a minute (equivalent to SEC.... )
MINsame as JAM
NILno (see NIL)
NPno problem
Oover to you
OOover and out
/another form of “over to you” (from x/y as “x over y”)
\lambda (used in discussing LISPy things)
OBTWoh, by the way
OTOHon the other hand
R U THERE?are you there?
SECwait a second (sometimes written SEC... )
SYNAre you busy? (expects ACK, SYN|ACK, or RST in return; this is modeled on the TCP/IP handshake sequence)
Tyes (see the main entry for T)
TNX 1.0E6thanks a million (humorous)
TNXE6another form of “thanks a million
TTBOMKto the best of my knowledge
WRTwith regard to, or with respect to.
WTFthe universal interrogative particle; WTF knows what it means?
WTHwhat the hell?
<double newline>When the typing party has finished, he/she types two newlines to signal that he/she is done; this leaves a blank line between 'speeches' in the conversation, making it easier to reread the preceding text.
YHTBTYou Had To Be There. Used of a situation which loses significant meaning in the telling, usually because it's difficult to convey tone and timing.
<name>:When three or more terminals are linked, it is conventional for each typist to prepend his/her login name or handle and a colon (or a hyphen) to each line to indicate who is typing (some conferencing facilities do this automatically). The login name is often shortened to a unique prefix (possibly a single letter) during a very long conversation.
/\/\/\A giggle or chuckle. On a MUD, this usually means 'earthquake fault'.
<gd&r>grinning, ducking, and running
BBLbe back later
BRBbe right back
HHOJha ha only joking
HHOKha ha only kidding
HHOSha ha only serious
IMHOin my humble opinion (see IMHO)
LOLlaughing out loud
NHOHNever Heard of Him/Her (often used in initgame)
ROTFrolling on the floor
ROTFLrolling on the floor laughing
AFKaway from keyboard
CU l8trsee you later
MORFmale or female?
TTFNta-ta for now
TTYLtalk to you later
OICoh, I see
rehihello again

Most of these are not used at universities or in the Unix world, though ROTF and TTFN have gained some currency there and IMHO is common; conversely, most of the people who know these are unfamiliar with FOO?, BCNU, HELLOP, NIL, and T.

The MUD community uses a mixture of Usenet/Internet emoticons, a few of the more natural of the old-style talk-mode abbrevs, and some of the ‘social’ list above; specifically, MUD respondents report use of BBL, BRB, LOL, b4, BTW, WTF, TTFN, and WTH. The use of rehi is also common; in fact, mudders are fond of re- compounds and will frequently rehug or rebonk (see bonk/oif) people. The word re by itself is taken as ‘regreet’. In general, though, MUDders express a preference for typing things out in full rather than using abbreviations; this may be due to the relative youth of the MUD cultures, which tend to include many touch typists and to assume high-speed links. The following uses specific to MUDs are reported:

CU l8ersee you later (mutant of CU l8tr)
FOADfuck off and die (use of this is generally OTT)
OTTover the top (excessive, uncalled for)
pplabbrev for “people
THXthanks (mutant of TNX; clearly this comes in batches of 1138 (the Lucasian K)).
UOK?are you OK?

Some B1FFisms (notably the variant spelling d00d) appear to be passing into wider use among some subgroups of MUDders.

One final note on talk mode style: neophytes, when in talk mode, often seem to think they must produce letter-perfect prose because they are typing rather than speaking. This is not the best approach. It can be very frustrating to wait while your partner pauses to think of a word, or repeatedly makes the same spelling error and backs up to fix it. It is usually best just to leave typographical errors behind and plunge forward, unless severe confusion may result; in that case it is often fastest just to type “xxx” and start over from before the mistake.

See also hakspek, emoticon.