What is Aggregation in MongoDB?

In MongoDb, the Aggregation operator is used to group the values from multiple documents together, such that it can perform a variety of operations on the grouped data to return a single result for example sum, average, minimum, maximum, etc are some of the operations performed on the grouped data to return a computed result. MongoDB provides three ways to perform aggregation: the aggregation pipeline, the map-reduce function, and single-purpose aggregation methods.