a.k.a. smiley, text face, happy face, sad face, frowny face
An emoticon is a sequence of typed characters that creates a rough picture of something, such as a facial expression. If you don't see the picture in the emoticon shown above, try tilting your head to the left-the colon represents the eyes, the dash represents the nose, and the right parenthesis represents the mouth. More commonly known as smileys and also referred to as "ASCII-grams," emoticons number in the hundreds and are used to indicate delight, sadness, or frustration. The most popular one is the smiling face shown above, which people use in e-mail or chat rooms to say, "If you could see me now, I'd be smiling."
The term "emoticon" literally means "an icon that represents emotion." Emoticons grew out of the need to display feeling in the two-dimensional, online, written world. When speaking face-to-face (F2F), a person's facial expressions help you understand the meaning of what he or she is saying. Emoticons are an attempt to bring that extra nuance to online communications by composing a face out of ASCII characters. Some emoticons don't require you to tilt your head to see them. There's a new group of ASCII icons called assicons, as well as another group, called straight-on smileys. There are also elaborate images, known as ASCII art. These are generally used in sig files.
Emoticons usually follow after the punctuation (or replace the punctuation) at the end of a sentence. An emoticon tells someone what you really mean when you make an offhand remark ;^)
Check out NetLingo's smileys page for a closer head tilting look, and use one for yourself 0*-)