Restricts the number of documents that pass through the $limit in the pipeline.
$limit takes a single numeric (positive whole number) value as a parameter. Once the specified number of documents pass through the pipeline operator, no more will. Consider the following example:
db.article.aggregate(
{ $limit : 5 }
);
This operation returns only the first 5 documents passed to it from by the pipeline. $limit has no effect on the content of the documents it passes.