From the Sanscrit for the incarnation of Godhead, an avatar is the 'body' you 'wear' in a virtual community - an animated, articulated representation of a human which represents you, the user, in any virtual environment. Some of the more sophisticated chat rooms provide the facility to 'chat' over the 'net via the visual representation of interacting human forms.

In Aussie English, it's the piccy under yer name. Muchie's x-ray, my tandem, etc.