"How far can we push the envelope?"

[G/A]

Hi,


i am a reader of pprune for a long time and today i registered, because i have got a question.

My mother is a translator, and is translating a book at the moment. Now she came to me and asked what the following expression means:
"in an expression borrowed from the world of aviation, "how far can we push the envelope"?"

I never heard this expression before, and i hope you cand help me. What does it mean, can someone please describe it?
What is meant with envelope?

I thought something like the limit, but what limits? The physical or technical limits?

Would be nice if someone could help me.

best regards
G/A