In digital signal processing, what does the term "envelope" refer to?

A) The maximum amplitude of a signal

B) The frequency spectrum of a signal

C) The smooth curve that outlines the extremes of a waveform

D) The time duration of the signal

Answer: C) The smooth curve that outlines the extremes of a waveform

Explanation: The envelope of a waveform represents the smooth curve that outlines its maximum and minimum amplitudes over time, providing insight into the modulation characteristics of the signal.