WordNet (r) 3.0 (2006):

emoticon
    n 1: a representation of a facial expression (as a smile or
         frown) created by typing a sequence of characters in
         sending email; ":-( and :-) are emoticons"

The Jargon File (version 4.4.7, 29 Dec 2003):

emoticon
 /ee?moh'ti?kon/, n.

    [common] An ASCII glyph used to indicate an emotional state in email or
    news. Although originally intended mostly as jokes, emoticons (or some
    other explicit humor indication) are virtually required under certain
    circumstances in high-volume text-only communication forums such as Usenet;
    the lack of verbal and visual cues can otherwise cause what were intended
    to be humorous, sarcastic, ironic, or otherwise non-100%-serious comments
    to be badly misinterpreted (not always even by newbies), resulting in
    arguments and flame wars.

    Hundreds of emoticons have been proposed, but only a few are in common use.
    These include:

    +-------------------------------------------------------------------------+
    |:-)|?smiley face? (for humor, laughter, friendliness, occasionally       |
    |   |sarcasm)                                                             |
    |---+---------------------------------------------------------------------|
    |:-(|?frowney face? (for sadness, anger, or upset)                        |
    |---+---------------------------------------------------------------------|
    |;-)|?half-smiley? ( ha ha only serious); also known as semi-smiley or  |
    |   |winkey face.                                                         |
    |---+---------------------------------------------------------------------|
    |:-/|?wry face?                                                           |
    +-------------------------------------------------------------------------+

    (These may become more comprehensible if you tilt your head sideways, to
    the left.) The first two listed are by far the most frequently encountered.
    Hyphenless forms of them are common on CompuServe, GEnie, and BIX; see also
    bixie. On Usenet, smiley is often used as a generic term synonymous
    with emoticon, as well as specifically for the happy-face emoticon.

    The invention of the original smiley and frowney emoticons is generally
    credited to Scott Fahlman at CMU in 1982. He later wrote: ?I wish I had
    saved the original post, or at least recorded the date for posterity, but I
    had no idea that I was starting something that would soon pollute all the
    world's communication channels.? In September 2002 the original post was
    recovered.

    There is a rival claim by one Kevin McKenzie, who seems to have proposed
    the smiley on the MsgGroup mailing list, April 12 1979. It seems likely
    these two inventions were independent. Users of the PLATO educational
    system report using emoticons composed from overlaid dot-matrix graphics in
    the 1970s.

    Note for the newbie: Overuse of the smiley is a mark of loserhood! More
    than one per paragraph is a fairly sure sign that you've gone over the
    line.


The Free On-line Dictionary of Computing (30 December 2018):

emoticon
:-)
smiley
smilies

    /ee-moh'ti-kon/ (Or "smiley") An ASCII glyph
   used to indicate an emotional state in text-only electronic
   messaging systems such as chat, electronic mail, SMS or
   news.  Although originally intended mostly as jokes,
   emoticons are widely recognised if not expected; the lack of
   verbal and visual cues can otherwise cause non-serious
   comments to be misinterpreted, resulting in offence, arguments
   and flame wars.

   Hundreds of emoticons have been proposed, but only a few are
   in common use.  These include:

    :-)	"smiley face" (for humour, laughter,
   	friendliness, occasionally sarcasm)

    :-(	"frowney face" (for sadness, anger, or upset)

    ;-)	"half-smiley" (ha ha only serious); also
   	known as "semi-smiley" or "winkey face".

    :-/	"wry face"

   These are more recognisable if you tilt your head to the left.
   The first two are by far the most frequently encountered.
   Hyphenless forms of them are also common.  The acronym "lol"
   is also often used in the same context for the same effect
   (and is easier to type).

   The emoticon was invented by one Scott Fahlman on the CMU
   bboard systems on 1982-09-19.  He later wrote: "I had no
   idea that I was starting something that would soon pollute all
   the world's communication channels."  GLS confirms that he
   remembers this original posting, which has subsequently been
   retrieved from a backup
   (http://research.microsoft.com/~mbj/Smiley/BBoard_Contents.html).

   As with exclamation marks, overuse of the smiley is a mark of
   loserhood!  More than one per paragraph is a fairly sure sign
   that you've gone over the line.

   [Jargon File]

   (2010-05-16)