Wissner-Gross defines intelligence as the ability to maximize future options. This is related to the concept of entropy well known in physics. Indeed, entropy is a measure of the number of specific ways in which a thermodynamic system may be arranged. Interestingly, life is not part of the equation. Even non living dynamic systems can be considered as having some degree of intelligence.
Alex Wissner-Gross: A new equation for intelligence (TED Nov. 2013)