MDR
Outsourced security operations: an external team watches, hunts and responds to threats in your environment around the clock, instead of you running the tools yourself.
Buying EDR or XDR software is only half the job — someone also has to watch it around the clock, triage alerts and act. Managed Detection and Response is that someone, sold as a service: the provider's analysts in a security operations center (SOC) run the tooling for you. Gartner popularized the term around 2016.
It differs from the older MSSP model, which mostly forwarded alerts; MDR emphasizes active threat hunting and hands-on response, not just monitoring. It fills the gap for organizations too small to staff their own SOC. Offerings include CrowdStrike Falcon Complete, Arctic Wolf and Sophos MDR.