Butterfly effect
The Butterfly effect is the essence of Chaos Theory. It holds that a system can be sensitve to intial conditions. Such systems can become unstable over time, such as the weather and gives rise to the notion that a Butterfly flapping its wings in New York can cause a hurricane in the pacific[1].
In Popular Culture
The butterfly effect is usually found in science fiction stories and movies. It describes the possibility of a person traveling back in time, and inadvertently changing some miniscule thing in the past — such as killing a butterfly — that has momentous consequences as time goes by, so that the he returns to a radically altered future.
Movies of this type include:
The Butterfly effect was also a central theme of Isaac Asimov's short story "A Sound of Thunder", in which a man travels back in time to hunt dinosaurs, and inadvertently shoots a butterfly by mistake. This scenario, while plausible enough as a science fiction story, could certainly never happen in real life.