A chatterbot (also chatbot, chatterbox) is a program which attempts to maintain a conversation with a person. While it is true that a good understanding of a conversation is required to carry on a meaningful dialog, most chatterbots do not attempt this. Instead they attempt to pick up cue words or phrases from the person which will allow them to use pre-prepared or pre-calculated responses which can move the conversation on in an apparently meaningful way without requiring them to know what they are talking about. An exception to this is Jabberwacky.
The classic early chatterbots are ELIZA, PARRY and SHRDLU. More recent programs are Racter and A.L.I.C.E.
See also: Turing test, Loebner prize
