eARC, also known as Enhanced Audio Return Channel, is an updated version of the current HDMI ARC, and is a feature of the new HDMI 2.1 standard. It functions just like the former ARC feature but will also support uncompressed advanced audio formats (Dolby Atmos, DTS:X, DTS-HD Master Audio, etc) for a better audio experience. In addition, with HDMI 2.1's faster data transfer and higher bandwidth, lip-sync between audio and video will be even more accurate.
For more information on ARC please see article AUDIO: ARC