“Then they discovered the time fracture. Where we could live without having to worry about the butterfly effect.” – Maddy Shannon, Terra Nova.
“The what?” – Joshua Shannon, Terra Nova.
“The butterfly effect, where something as small as stepping on a butterfly could change the whole course of time.” – Maddy Shannon, Terra Nova.
The exchange you read above is from a time travel show called Terra Nova. A family (somewhat illegally) travel through time to a village (made of 21st-century people) that was developed in a time fracture. A time fracture is like a parallel universe where what people do doesn’t affect the already established world.
The butterfly effect is (as explained above) when something as small as plucking a blade of grass can change the course of the future. That blade of grass could have fed the cow that fed your family. What if that cow was the difference between life and death for that cow? What if that cow fed died and didn’t feed your family.