Pipeline aggregations, as their name suggests, allow you to aggregate over the results of another aggregation. They let you pipe the results of an aggregation as input to another aggregation. Pipeline aggregations are a relatively new feature, and they are still experimental. At a high level, there are two types of pipeline aggregation:

• Parent pipeline aggregations have the pipeline aggregation nested inside other aggregations
• Sibling pipeline aggregations have the pipeline aggregation as the sibling of the original aggregation from which pipelining is done

Let's look at how the pipeline aggregations work by considering one example of cumulative sum aggregation, which is a parent of pipeline aggregation.