What is EDR, and how is it different from antivirus?

Antivirus (and next-gen AV/EPP) focuses on prevention — blocking malware before it runs. Endpoint Detection and Response (EDR) assumes some threats will get through, so it continuously records what's happening on each device, detects suspicious behaviour, and gives you the tools to investigate and respond — isolating a host, killing a process or rolling it back. In practice the two work together: prevention reduces the volume, EDR catches and contains what slips past.