thesaurus.maths.org

A system, usually in dynamics, is chaotic if:
- it is predictable in principle;
- what happens to it in the long run depends very sensitively on how it is set up in the first place, which makes it very hard to predict in practice
- there is usually some way of describing the general types of long-term behaviour, like a 'strange attractor'.
For instance, the weather, or the movements of three stars around one another, are chaotic systems.