Definition: Facebook’s results metric is a number representing the amount of times your ad achieved a specific outcome, which is based on the campaign objectives and settings.
How it’s used: The Facebook results metric highlights your campaign’s performance based on what business objectives and settings you selected. This enables you to compare performance amongst campaigns with similar objectives and identify opportunities and areas that you can optimise for better results.
Your campaign and the ad account settings will determine how you are billed for an ad. For example, while you may have chosen Conversions as the campaign objective and the result is the number of purchases that were made, you may be charged for the number of impressions each ad receives.