1. the phenomenon whereby a small change at one place in a complex system can have large effects elsewhere, e.g., a butterfly flapping its wings in Rio de Janeiro might change the weather in Chicago;
WordNet (r) 3.0 (2006):
butterfly effect
n 1: the phenomenon whereby a small change at one place in a
complex system can have large effects elsewhere, e.g., a
butterfly flapping its wings in Rio de Janeiro might change
the weather in Chicago