Conversion rate refers to the percentage of visitors to a webpage or recipients of a marketing message who take a specific action (also known as a "conversion") as a result of seeing a display ad. This action could be anything that the advertiser considers to be a desired outcome, such as making a purchase, filling out a form, or downloading an app.

To calculate the conversion rate for a display ad campaign, the number of conversions generated by the ad is divided by the number of visitors to the webpage or recipients of the marketing message who saw the ad. The resulting percentage is the conversion rate.

For example, if a display ad generates 100 conversions out of 1,000 visitors, the conversion rate would be 10%.

Advertisers may track conversion rate as a way to evaluate the performance of their display ad campaigns and to identify areas for improvement. They may also track other metrics related to conversions, such as the cost per conversion (CPC) and the return on investment (ROI) of their campaigns. Optimizing these metrics can help advertisers improve the effectiveness of their display ad campaigns and increase the number of conversions generated by their ads.