Three terms, two ideas
Endpoint detection and response (EDR) is a technology. An agent on each device records activity, detects suspicious behaviour and lets analysts investigate and contain a host remotely.
Extended detection and response (XDR) is also a technology. It widens the same idea by correlating endpoint data with other sources such as identity, email or network telemetry. The sources included differ by product, so the label alone does not tell you what is covered.
Managed detection and response (MDR) is a service. A provider operates detection and response on your behalf, usually on top of an EDR or XDR product.
Questions that decide it
Start with the team, not the product. A detection tool is only as useful as the people who respond to its alerts.
- Who will triage alerts at 02:00, and what are they allowed to do without approval?
- Which non-endpoint sources do you already have that would improve investigations?
- Do you need to keep data in a particular region or on your own infrastructure?
- How many different device and server types must the agent support?
A practical sequence
Most organisations get the best result by fixing endpoint coverage first, then adding the data sources that their analysts ask for during real investigations. If you cannot staff round-the-clock response, evaluate a managed service as a separate decision rather than assuming a more expansive product will close the gap.