The “butterfly effect” is based on the statement “a butterfly flapping its wings in (insert place A) can cause a hurricane/tornado/etc. in (insert place B, which is far away from place A).”
In theory it kind of makes sense. If weather conditions are balancing on a knife-edge, and even the slightest factor could influence things one way or another, maybe a butterfly wing-beat could be the straw that breaks the camel’s back, triggering a tornado.
And while the above scenario does sound far fetched, the butterfly effect is actually something that is familiar to many kinds of scientists.