A:Answer While I don't own this, I have been looking at it for a while, and yes, one is an ARC HDMI.
They're used with sound bars, or sound plates, like I have. Got three things plugged into the Sound plate, Cable, BlueRay, and Roku, and one HDMI goes to the ARC input, if you've got one. I don't on my current TV, and that just means I use an optical audio cable. It returns the sound back to the sound bar, or sound system.
Basically, ARC allows for a two-way connection, say the Cable sends its signal through my sound plate, to the television, then ARC sends the sound back to the plate.
It also has some trading data features on it. Honestly I think it is used when you just plug stuff right into the television, like a DVD player, in transferring the sound to be playing back to the device, because the way mine is set up, three of my devices go through the Sound device anyway, and I'm pretty sure that is when the audio is picked up to be played.
