Frequency capping gives advertisers the ability to specify a limit to the number of:

Frequency capping gives advertisers the ability to specify a limit to the number of:

  • clicks for all users
  • impressions for all users
  • impressions for a unique user
  • clicks for a unique user

The correct Answer is:

  • impressions for a unique user

Explanation: Frequency is the average number of times a unique user sees your ad in a position of “1” over a given time period. Use frequency capping to help control the maximum number of times that you’d like each person to see your ad on the Display Network.

Read more here: https://support.google.com/adwords/answer/117579?hl=en