HDMI ARC (Audio Return Channel) allows audio to travel back from your TV to a soundbar or AV receiver through the same HDMI cable that carries picture to the TV — eliminating the need for a separate optical audio cable. To use it, simply connect your soundbar to the HDMI port labelled "ARC" on your TV.
No special HDMI ARC cable is required — any standard High Speed HDMI cable will support ARC. The newer eARC (enhanced Audio Return Channel), found on HDMI 2.1 ports, delivers higher-quality audio including uncompressed Dolby Atmos and DTS:X. For eARC, an HDMI 2.1 cable is recommended to get the full benefit, though many HDMI 2.0 cables will also work in practice.