Each sponsored search ad that a user sees is called a(n):

An impression is counted each time a sponsored search ad is displayed to a user, regardless of whether the user interacts with it. This metric indicates the ad's visibility. A click occurs when a user actively selects the ad, leading them to the advertiser's landing page. CTR (Click-Through Rate) is a ratio calculated by dividing the number of clicks by the number of impressions, indicating the ad's effectiveness in attracting user interest. A conversion is a desired action taken by a user after clicking an ad, such as a purchase or form submission, representing a valuable outcome for the advertiser.