Envelope - Definition
envelope
n 1: a flat (usually rectangular) container for a letter, thin
package, etc.
2: any wrapper or covering
3: a curve that is tangent to each of a family of curves
4: a natural covering (as by a fluid); "the spacecraft detected
an envelope of gas around the comet"
5: the maximum operating capability of a system (especially an
aircraft); "test pilots try to push the envelope"
6: the bag containing the gas in a balloon [syn: envelope,
gasbag]