AI is not a very well defined term - according to my AI textbook there are 4 main definitions of AI
-"[The Automation of] activities that we associate with human thinking, activities such as decision-making, problem solving, learning..." (Bellman, 1978)
ie: Think/reason like a human
-"The study of the computations that make it possible to perceive, reason, and act" (Winston, 1992)
ie: Think reason perfectly rationally
-"The study of creating machines that perform functions that require intelligence when performed by people" (Kurzweil, 1990)
ie: Behave/act like a human
-"A field of study that seeks to explain and emulate intelligent behavior in terms of computational processes" (Schalkoff, 1990)
ie: Behave/act perfectly rationally
Taken from "Artificial Intelligence: A Modern Approach" by Russell, Norvig
AI can be applied to anything that requires decisions to be made.