Definition of envelopes:
(n) :
A paper or cardboard wrapper used to enclose small, flat items, especially letters, for mailing.
(n) :
Something that envelops; a wrapping.
(n) :
A bag containing the lifting gas of a balloon or airship; fabric that encloses the gas-bags of an airship.
(v) :
(transitive, rare) To put (something) in an envelope.
(n) :
(electronics) A curve that bounds another curve or set of curves, as the modulation envelope of an amplitude-modulated carrier wave in electronics.
(n) :
(music) The shape of a sound, which may be controlled by a synthesizer or sampler.