TITLE: What's the opposite of damping?
QUESTION [6 upvotes]: A colleague asked me this question and I had no clue.  

When a function (for instance, a sine wave) is multiplied by a decaying exponential, we call the phenomenon damping.  What would it be called if the wave is multiplied by a growing exponential?  

I suggested forcing or driving, since functions of that form arise in simple harmonic oscillators driven by sine waves with frequency equal to the oscillator's frequency.  But I wondered if others had words for it.

REPLY [2 votes]: I would call reinforcing and amplifying a signal positive feedback, and where you have neither dampening nor feedback I would call that resonance or ringing.