CPM measures the cost per 1,000 impressions. It’s a good metric to evaluate competition level and costs to reach your audience.
Custom Metric
Advertisers can create custom metrics that combine existing metrics with a mathematical formula. That formula can be based on Meta’s current ads metrics, standard events, custom events, and custom conversions.
Estimated Audience Size
Estimated Audience Size estimates how many Accounts Center Accounts (previously defined as users) are eligible for targeting given the settings in your ad set.
Event Responses
The number of people who responded ‘Interested’ or ‘Going’ to your Facebook event and credited to your ads.
Impressions
Impressions are the number of times your ads were displayed to your target audience. Impressions aren’t counted if it is detected they came from bots.