Part 4 of a 5-part series on the origin of popular phrasesWhen you're innovative, we say you're trying to "push the envelope."
The phrase originates from the go-go days of aviation.
The "flight envelope" is a math formula that describes the upper and lower limits of the factors affecting safe flight, such as a plane's speed and altitude.
Daredevil pilots spoke of their urge to "push the envelope" by testing those limits.
The phrase moved into popular use after novelist Tom Wolfe included it in his 1979 book, The Right Stuff.
