A set of limits for the performance capabilities of some type of machine, originally used to refer to aircraft; -- it is often described graphically as a two-dimensional graph of a function showing the maximum of one performance variable as a function of another. Now it is 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.
An encasement of a living object with a nebulous, formless quality or tenuous matter whose light, color and tone tend to give indication of the personality, vitality and being of the object surrounded.