Intel AMT allows redirecting graphics output and keyboard/mouse/USB input over network connection. It's like a hardware device connected to HDMI port to capture screen and to USB ports to send inputs, but it's built right into the motherboard. It doesn't spawn a process in the operating system or use resources to any meaningful degree. The OS knows about AMT only what the hardware tells it, if anything at all.

Unlike software-based remote desktop solutions (VNC, TeamViewer), it's independent from the operating system. As long as the system is connected to power, AMT can run. You can log into a fully shut down computer, power it on and see boot logos and access BIOS before the OS even begins to load. You can use AMT to install operationg system on a PC with completely empty hard drive by virtually attaching a CD/DVD or USB install media.

It's extemely powerful management interface, but it's close-sourced and has a history of serious security flaws.