Envelope (disambiguation)

An envelope is a flat, folded paper container often used for mailing things.
An envelope is a set of headers for an e-mail
An envelope is a mathematical curve, surface, or higher dimensional object defined as being tangent to a given family of lines or curves (or surfaces, or higher dimensional objects, resp.).
An envelope is a curve that bounds another curve or set of curves, as the modulation envelope of an amplitude-modulated carrier wave in electronics. See envelope detector.
An envelope is the shape of a sound which may be controlled by a synthesizer or sampler in music, derived from the above definition for electronics.
An envelope is the outer layer of some viruses.

at present see Virus#Viral_structure_and_anatomy

In aerospace, an envelope is the limits within which an aircraft can operate.
The envelope paradox is a paradox in probability.