It is API compatible with MongoDB, document database.
Now there is Amazon DocumentDB, that is API compatible with MongoDB :)
AWS Launches New Document-Oriented Database Compatible with MongoDB @InfoQ
"Some speculate that DocumentDB is built upon AWS Aurora PostgreSQL, but it's clear that it's NOT running MongoDB software. MongoDB, Inc is one of a handful of companies that have recently changed their license to discourage cloud providers from offering parts of their open-source software as a service."