a computer program, running on someone's computer (often, but not exclusively, in a university), designed for the purpose of Internet chatting
a cross between a MUD and an IRC (without the role playing of MUDs and without a real-time chat room )
a way to chat on the Internet by using only text
A talker is similar to a MUD only it involves more social interaction than a MUD. One of the most popular Talker systems is Nuts (by Neil Robertson), all though there are many other systems like IForms, and many many Nuts rewrites.
n. An Internet-based synchronous communication mechanism most commonly used to support multiuser chat functions. Such systems typically provide specific commands for movement through separate rooms, or chat areas, and allow users to communicate with other users in real time through text messages, indicate simple gestures, use a bulletin board system (BBS) for posting comments, and send internal e-mail. See also BBS (definition 1), chat1 (definition 1).