This was previously known as threat explorer. Threat explorer is a jumping off point to Office 365 Analytics that promises to help you identify and understand anomalous behavior in your Office 365 tenant.
You can also configure alerts and respond as needed. Much of this is now also displayed in the Alerts section, as described earlier.
Once Office 365 Analytics is enabled, threat explorer gives you the ability to review activities that have been identified by the system as potentially dangerous, such as malware being sent by email.
