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, reviewCount for the number of underlying ratings, and bestRating and worstRating to define the scale. 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, Service or LocalBusiness.