/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.
:-) "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.