Which of the following describes the number of times a unique user will see an ad over a given time period?

The selection Frequency is correct because it specifically measures the average number of times a unique user is exposed to an advertisement within a specified timeframe. While "Reach" counts the total number of unique individuals who saw the ad and an "Impression" counts every single instance the ad was displayed regardless of the viewer, Frequency provides the essential ratio of impressions to reach ( Frequency=ImpressionsReach Frequency= Reach Impressions ), allowing advertisers to manage ad fatigue and ensure their message is seen enough times to drive brand awareness or conversion without over-saturating the audience.