What is the Audio Return Channel (ARC) feature?

HDMI ARC (Audio Return Channel) and eARC explained - FlatpanelsHD

ARC - the audio return channel of HDMI - FeinTech

Do You Know How To Get The Best Out Of An ARC HDMI Channel – channelnews

Panasonic - Television - Function - How to set up the ARC Audio Return Channel feature.

HDMI Audio Return Channel (ARC) feature

HDMI ARC and eARC: Audio Return Channel for beginners - CNET

How to activate the Audio Return Channel (ARC) feature

What Are HDMI 2.1 ARC and eARC Cables? - Dolby - Dolby

Can someone explain to me how on earth HDMI ARC is supposed to work? - Streaming Audio - Naim Audio - Community