History: What does the cutoff parameter do?

What does the cutoff parameter do?

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