The science of Artificial Intelligence (AI) might be defined as the construction of intelligent systems and their analysis. A natural definition of systems is anything which has an input and an output stream. Intelligence is more complicated. It can have many faces like creativity, solving problems, pattern recognition, classification, learning, induction, deduction, building analogies, optimization, surviving in an environment, language processing, knowledge and many more. A formal definition incorporating every aspect of intelligence, however, seems difficult. An important observation is that most, if not all known facets of intelligence can be formulated as goal driven or, more precisely, as maximizing some utility function. It is, therefore, sufficient to study goal driven AI. E.g. the (biological) goal of animals and humans is to survive and spread. The goal of AI systems should be to be useful to humans. The problem is that, except for special cases, we know neither the utility function, nor the environment in which the system will operate, in advance. The mathematical theory, coined AIXI, (see next item) represents a formal solution of these problems. Artificial Intelligence Homepage of Marcus Hutter
The best description of AI is that humans do not make very good examples.