The output format translates the final key/value pair from the reduce function and writes it out to a file by a record writer. By default, it will separate the key and value with a tab and separate records with a newline character. This can typically be customized to provide richer output formats, but in the end, the data is written out to HDFS, regardless of format. Not only is writing to HDFS supported by default but also output to Elasticsearch index, output to RDBMS, or a NoSQL such as Cassandra, HBase, and so on.