The term dialogue system is widely used nowadays to refer to automatic systems involving coherent dialogue with a human interlocutor. The editors of the Journal of Dialogue Systems define a dialogue system as:
A computational device or agent that (a) engages in interaction with other human and/or computer participant(s); (b) uses human language in some form such as speech, text, or sign; and (c) typically engages in such interaction across multiple turns or sentences (http://www.jods.org/).
This definition highlights several important aspects of such systems. A dialogue system always has a user, who interacts with the system for a specific goal such as completing some tasks. The interaction involves a conversation in human language between two or more participants and can take several turns. The fact that human language is used in the interaction differentiates the field from other fields such as database access using computer languages (such as SQL) or interaction between software agents that communicate using XML or some other standard computer formats.