The short explanation
Consumer Electronics Control is a low-speed control channel that runs inside the HDMI cable alongside the video. Devices use it to send simple commands: turn on, go to standby, switch to this input, volume up.
Nearly every manufacturer renames it. Anynet+, Bravia Sync, Simplink, Viera Link, EasyLink and a dozen others are all CEC.
Where you run into it
When it works it is genuinely convenient. When it does not, it produces the most confusing symptoms in home cinema: devices waking each other in a loop, an input switching itself back, a system that powers on when you turn off the lights. Implementations vary widely between brands, and a chain of four devices from four manufacturers is where the trouble usually starts.
If a system behaves like it has a mind of its own, turning CEC off on each device one at a time is a fast diagnosis.
How the DR HDMI 8K handles it
The DR HDMI 8K lists CEC support for inter-device control between the equipment on its input and output, so CEC does not have to be given up when the unit joins the chain.
Want to test your own HDMI chain?
The DR HDMI 8K is sold through the HDFury.eu web shop.