envelope
noun [ C ]
WORKPLACE uk/ˈenvələʊp/ usa flat, usually square or rectangular, paper container for a letter:
a brown/manila envelope
a sealed envelope
a flat, usually square or rectangular, plastic container used for keeping papers in:
The papers were handed to me in a transparent plastic envelope.
push the envelope
to go further than the usual limits by doing something new, dangerous, etc.:
We're really pushing the envelope on this technology; a lot of other companies are just playing catch-up.
See also
padded envelope
prepaid envelope
self-addressed envelope
self-addressed stamped envelope
stamped addressed envelope