HDMI is a manufacturer-independent interface for transmitting (primarily) video signals. Abbreviation for "High Definition Multimedia Interface".
With only one cable, pictures and sounds are transmitted simultaneously. This leaves nothing to be desired in terms of audio and picture quality. The latest versions even support image resolutions of up to 4096 × 2560 pixels and additionally transmit up to eight audio channels - a real revolution in the consumer sector.
Meanwhile, modern HDMI cables can do much more than just transmitting pictures and sound in the best digital quality - the additional functions of HDMI ARC and HDMI CEC are explained here -> ARC/CEC.