Endpoint detection and response (EDR) is the latest industry term that describes what used to be called antivirus. EDR is installed on endpoint devices and attempts to identify known signatures and erratic behaviors that might be indicative of malicious code.  Managed detection and response (MDR) is a managed service whereby security analysts in a security operations center (SOC) are actively monitoring, hunting, detecting, and quarantining malicious activity. As such, EDR is more tool-based, whereas MDR is more tool and people based.  Both EDR and MDR are essential, and they work nicely together, especially when the telemetry from the EDR agent can be ingested into the MDR process.