envelope Meaning, Definition & Usage

noun a flat (usually rectangular) container for a letter, thin package, etc.
noun any wrapper or covering
noun a curve that is tangent to each of a family of curves
noun a natural covering (as by a fluid)
- the spacecraft detected an envelope of gas around the comet
noun the maximum operating capability of a system (especially an aircraft)
- test pilots try to push the envelope
noun the bag containing the gas in a balloon
gasbag.

F. enveloppe.

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.
(Astron.) The nebulous covering of the head or nucleus of a comet; -- called also coma.
(Fort.) A work of earth, in the form of a single parapet or of a small rampart. It is sometimes raised in the ditch and sometimes beyond it. Wilhelm.
(Geom.) A curve or surface which is tangent to each member of a system of curves or surfaces, the form and position of the members of the system being allowed to vary according to some continuous law. Thus, any curve is the envelope of its tangents.
A set of limits for the performance capabilities of some type of machine, originally used to refer to aircraft. Now also used metaphorically to refer to capabilities of any system in general, including human organizations, esp. in the phrase push the envelope. It is used to refer to the maximum performance available at the current state of the technology, and therefore refers to a class of machines in general, not a specific machine.