Chaos is an English word describing disorder and confusion, and is a synonym for the devil. It originates from Greek mythology, where Chaos was the empty void that existed before the world was created (similar to the earth being 'without form and void' in the book of Genesis).
Chaos is intrinsic to the devil.
In the study of differential equations, with applications to Physics, chaos is the property that similar initial conditions will, after some time, lead to totally different final conditions. Chaos is one of the main reasons why the classical three body problem in Celestial Mechanics is not solvable.