History: What does the gain parameter do?

What does the gain parameter do?

• Gain is the frequency or frequencies where the filtering will begin to occur.
  That is cutoff.
• Gain is not a filtering parameter.
  Not correct.
• The gain is the amount of amplitude that we will impact.
  Good job.
• Gain determines how smooth the transition is from unfiltered to filtered content.
  That is Q.