Generally speaking, an avatar is the embodiment of a person or idea. However, in the computer world, an avatar specifically refers to a character that represents an online user. Avatars are commonly used in multiplayer gaming, online communities, and web forums.
Online multiplayer role-playing games (MMORPGs) such as World of Warcraft and EverQuest allow users to create custom characters. These characters serve as the players' avatars. For example, a World of Warcraft player may choose a Paladin with blue armor as his avatar. As the player progresses in the game, his character may gain items and experience, which allows the avatar to evolve over time.
Avatars are also used in online communities, such as Second Life and The Sims Online. These avatars can be custom-designed to create a truly unique appearance for each player. Once a user has created an avatar, he or she becomes part of an online community filled with other users' avatars. Players can interact with other avatars and talk to them using text or voice chat. It's no surprise that "Second Life" refers to a virtual life that players live through their avatars.
Finally, avatars are common in web forums. Online discussion boards typically require users to register and provide information about themselves. Many give users the option to select an image file that represents the user's persona. This image, combined with a made-up username, serves as a person's avatar. For example, a user may select a picture of a Pac-Man and choose the name "pac32" for his avatar. This avatar typically appears next to each posting the user contributes in an online forum.
Regardless of the application, avatars allow people to represent themselves online in whatever way they want. They may be considered alter-egos, since users can customize characters that are completely different than their actual personas. Of course, what's the point of having a "second life" if it's the same as reality?