Chaos Theory is the qualitative study of unstable aperiodic behaviour in deterministic non-linear dynamical systems. (Source - http://www.exploratorium.edu/complexity/lexicon/chaos.html)
See also:
Entropy, Formalism, Stochastic MusicBibliography: DI SCIPIO, Agostino (1991). Caos deterministico, composizione e sintesi del suono

