Oracle Enterprise Manager (=OEM) is a versatile management tool that is used to monitor and manage IT infrastructures. It is therefore a central platform for monitoring and controlling databases, applications and hardware.
Monitoring
OEM can be used to monitor databases for performance and availability, for example. This also makes it possible to detect and rectify problems at an early stage.
Administration
Databases can also be configured and managed using OEM
Automation
Tasks can be automated in OEM, such as backup jobs
Information about Oracle Enterprise Manager can be found here: https://www.oracle.com/enterprise-manager/