That which envelops, wraps up, encases, or surrounds; a wrapper; an inclosing cover; esp., the cover or wrapper of a document, as of a letter.
- A flat paper container, especially for a letter, usually having a gummed flap.
- Something that envelops; a wrapping.
- Biology An enclosing structure or cover, such as a membrane or the outer coat of a virus.
- The bag containing the gas in a balloon or airship.
- The set of limitations within which a technological system, especially an aircraft, can perform safely and effectively.
- The coma of a comet.
- Mathematics A curve or surface that is tangent to every one of a family of curves or surfaces.
- push the envelope To increase the operating capabilities of a technological system.
- push the envelope To exceed the existing limits in a certain field; be innovative.