History: What does an Inverse FFT do?

What does an Inverse FFT do?

• Changes the analysis from amplitude over frequency to frequency over amplitude.
  That doesn't make sense.
• Returns from analysis to sound.
  Perfect.
• Changes the analysis from frequency over amplitude to amplitude over frequency.
  That doesn't make sense.
• Breaks down the sound into windows of amplitude over frequency.
  That would be a regular FFT.