Antimalware Service is a programme that runs on your computer. Windows 10 Professional x64 Bitd

Bitdefender TS 2016 is installed and functioning on my computer.

Why does Windows Task Manager display the process "antimalware service executable" running (and using a lot of CPU) on a regular basis?

Isn't this anything to do with Windows Defender?

When a third-party AV is active, I assumed WD is inactive.