Differ compares the documents in the source index to those in the destination index.

Created means that a document has been added to the destination that didn't exist in the source index.

Deleted means that a document has been found in the source index but it doesn't exist in the destination index.

Unchanged means that a document has not been changed between source and destination index.

Updated means that a document has been found both in the source and destination index, but its contents (_source) has changed.

Diff is the outcome of comparing two documents in source and destination index.

Document is a generic document retrieved from Elasticsearch.

Mode describes the outcome of comparing two documents.