An emoticon is a pictorial representation of a facial expression using punctuation marks, numbers and letters, 
usually written to express a person's feelings or mood.
Emoticons are often used to alert a responder to the tenor or temper of a statement, and can change and improve interpretation of plain text. The word is a portmanteau word of the English words emotion and icon. In web forums, instant messengers and online games, text emoticons are often automatically replaced with small corresponding images, which came to be called emoticons as well.
A famous emoticon is ":D", which represents laughing.