- An envelope is a flat, folded paper container often used for mailing things.
- The envelope of an e-mail contains the information used for routing and is passed along the e-mail without being part of the actual message.
- 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
