蝴蝶效应是指在一个动态系统中，初始条件下微小的变化能带动整个系统的长期的巨大的连锁反应，是一种混沌的现象。“蝴蝶效应”在混沌学中也常出现。

「蝴蝶效应」是连锁效应的其中一种，其意思即一件表面上看来毫无关系、非常微小的事情，可能带来巨大的改变。此效应说明事物发展的结果，对初始条件具有极为敏感的依赖性，初始条件的极小偏差，将会引起结果的极大差异。

The butterfly effect refers to a concept that small causes can have large effects. Initially, it was used with weather prediction but later the term became a metaphor used in and out of science.

In chaos theory, the butterfly effect is the sensitive dependence on initial conditions in which a small change in one state of a deterministic nonlinear system can result in large differences in a later state. The name, coined by Edward Lorenz for the effect which had been known long before, is derived from the metaphorical example of the details of a hurricane (exact time of formation, exact path taken) being influenced by minor perturbations such as the flapping of the wings of a distant butterfly several weeks earlier. Lorenz discovered the effect when he observed that runs of his weather model with initial condition data that was rounded in a seemingly inconsequential manner would fail to reproduce the results of runs with the unrounded initial condition data. A very small change in initial conditions had created a significantly different outcome.