Stochastic means that its a system whose probabilities don't evolve with multiple interactions/events. Mathematically, all chaotic systems are stochastic (I think) but not vise versa. Or another way to say it is that in a stochastic system, all events are probabilistically independent.

Yes, its a hard to define word. I spent 15 minutes trying to define it to someone (who had a poor understanding of statistics) at a conference once. Worst use of my time ever.