A name given in affectionate familiarity, sportive familiarity, contempt, or derision; a familiar or an opprobrious appellation; as, Nicholas's nickname is Nick.
A name chosen by a Jabber User as a convenient moniker for use when Chatting. A user's nickname is not necessarily the same as that their username. In the context of Groupchat, we use the term Room Nickname.
The name you use on message boards. It's generally a good idea to pick one and stick with it at every forum you post at, since it will help you build up a reputation and help other webmasters become familiar with you.