Smiley, or happy face, is a stylized representation of a smiling human face, commonly represented as a yellow circle (or sphere) with two dots representing eyes and a half circle representing the mouth. “Smiley” is also sometimes used as a generic term for any emotion.
The emoticons on the Internet can largely be traced back to a proposal by Scott Fahlman in a message of 19 September 1982.
In web forums, instant messengers and online games, text emoticons are often automatically replaced with small corresponding images, which came to be called "Emoticons." Similarly, in some versions of Microsoft Word, the Auto Correct feature replaces basic smileys such as :-) and :-( with a single smiley-like character
Many sites use GIF or PNG graphic files, because of their transparency and small file size capabilities. Files can be created using a raster graphics editor. Many emoticon artists design their emoticons pixel by pixel. Some emoticons are made in vector format, such as SVG, and automatically processed using a graphics library. This allows SVG files to be automatically rendered as a GIF or PNG file, which is compatible with most browsers, which SVG is not. (Wikipedia).