envelope (EN)

noun

noun “envelope”

1. a flat paper container with a sealable flap, used to enclose a letter or document
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   She wrote a letter to her friend, placed it in an envelope, and mailed it the next day.
2. a layer or covering that surrounds or encloses something
   The spacecraft heated up as it passed through the envelope of Earth's atmosphere during re-entry.
3. the balloon-like part of an airship or hot air balloon that contains the gas
   They carefully folded the hot air balloon's envelope after landing.
4. (engineering) the range of capabilities or performance limits of a system or device
   The new engine design extends the performance envelope of the car, allowing it to reach higher speeds safely.
5. (electronics) a curve that shows how the amplitude of a signal changes over time
   The engineer studied the signal's envelope on the oscilloscope to diagnose the issue.
6. (music) the way a sound's loudness or tone changes over time from when it starts to when it stops
   The musician adjusted the envelope of the synthesizer, altering how each note began and faded away.
7. (mathematics) a curve or surface that is tangent to each one of a family of curves or surfaces
   In calculus class, they learned how to find the envelope of a set of lines, which represents their common tangents.
8. (biology) a membrane or layer that encloses an organ, cell, or virus
   The virus's outer envelope allows it to attach to and enter host cells.
9. (astronomy) a cloud of gas that surrounds a star or comet
   The comet's bright envelope became visible through the telescope as it approached the sun.
10. (computing) information added to a message that helps in its delivery but is not part of the message itself
    The email server reads the envelope of the message to determine where to deliver it.