The concept of Artificial Intelligence (AI) can be easily defined as the intelligence exhibited by an artificial (non-natural) entity.

Then comes the harder part of the question: What Is Intelligence? (I will try to discuss this hard question with my own point of view later on.)

Watch Professors Kevin Warwick and Noel Sharkey discussing artificial intelligence:

Note: AI is also used as a term to refer to a major branch of computer science, dealing with AI. (Well, please note that this is not a recursive definition.)

References:
* http://www-formal.stanford.edu/jmc/whatisai/whatisai.html
* http://www.silicon.com/technology/software/2010/02/08/artificial-intelli...