What type of output does the $out stage generate?

The $out stage in MongoDB is designed specifically to generate a new collection containing the results of the aggregation pipeline. When the $out stage is utilized, it takes the documents produced by the pipeline and writes them into a new collection, which can be referenced later for further querying or processing. This capability is particularly useful for storing and managing the results of complex aggregations or transformations of data, allowing users to work with the outputs in a structured way.

When using $out, if the collection already exists, it will be dropped and replaced with the new set of documents derived from the aggregation. This ensures that the output collection always contains the latest results based on the preceding stages of data processing. Thus, the key function of $out is to facilitate the creation and management of new or refreshed collections based on aggregation results.