whose variations are not random but look random. I shall use the term chaos to refer collectively to processes of this sort—ones that appear to proceed according to chance even though their behavior is in fact determined by precise laws.
The situation is further complicated because several other terms, notably nonlinearity, complexity, and fractality, are often used more or less synonymously with chaos in one or several of its senses.
It seems appropriate to call a real physical system chaotic if a fairly realistic model, but one with the system's inherent randomness suppressed, still appears to behave randomly.
before one can develop a rigorous theory dealing with some phenomenon, one needs an unambiguous definition of the phenomenon.