Pipeline aggregation allows for querying, aggregating, and transforming data in multiple stages in real-time through a single API request. While query arguments allow for making simple, single-stage queries through the API, pipelines allow for more complex searches, aggregations and transformations.
To leverage pipeline aggregation via the API, simply pass a pipeline query argument with the request. The pipeline query argument is an array of pipeline stages that execute in order. Each stage transforms the result set and passes it on to the next stage in the pipeline.