= Advertiser Outcome Score. AOS is a metric introduced by Facebook to optimize the effectiveness of ads within the social media network. The AOS can be viewed within Facebook's ad network and provides information about how often an ad is clicked and then an action such as installing a app, purchasing a product or registering online has been performed.

Performance indicators

Depending on the AOS there are two terms Cost-per-Mille (CPM) and conversion rate. High scores mean good ad placement, higher CPM and a higher conversion rate for advertisers.