AggregateRating (schema.org)
The schema.org type AggregateRating represents the average value of several user ratings and therefore describes, unlike Rating, not a single rating but a statistical summary.
In practice
The central properties are ratingValue for the average, itemReviewed for the item being rated, and ratingCount or reviewCount for the number of underlying ratings; bestRating and worstRating define the scale and are needed as soon as it differs from one to five. AggregateRating should only be used where genuine user ratings actually exist: invented or extrapolated values breach Google's guidelines and can lead to manual actions. The type is usually combined with Product or LocalBusiness. Note that Google excludes pages on which the business being reviewed controls the reviews about itself from the star display – for LocalBusiness and all other Organization types. For Service, Google provides no review snippets at all.