An avatar is a graphical representation of a user
An avatar is a graphical representation of a user, which may be a portrait or other art asset the user connects with on some level.
In other cases, or sometimes as a fallback, an avatar may be randomly assigned or be generic in nature (such as a silhouette of a human).
The avatar's purpose is to distinguish that user from others, allowing for easier recognition of what user's information is being displayed at any given time. This is often found in author bios, comments, membership-based sites, and discussion boards/forums.