To stretch established limits, as in technological advance or social innovation.
The phrase has its origins in the world of aviation, where ‘envelope’ has, since at least the late 60s, had the meaning ‘a set of performance limits that may not be safely exceeded.’ Test pilots are often called on to ‘push’ a new aircraft’s performance envelope by going beyond known safety limits, as in determining just how fast an airplane can be flown. In 1979 Tom Wolfe’s best-seller ‘The Right Stuff’ vividly described the life of test pilots during the 50s and 60s, and it appears that this book, and the subsequent movie, did much to popularize the notion of pushing the envelope. [Stuart Leichter reports that the words used in the movie are “pushing the outside of the envelope”;
The idea of an envelope as a kind of enclosing boundary is of course not new. In 1899 Arnold Bennett wrote: ‘My desire is to depict the deeper beauty while abiding by the envelope of facts.’