While most modern soundbars rely on an HDMI cable to connect to HDTVs ... 1980s—will have these familiar-looking RCA plugs situated on their rear input/output panels, which can deliver analog ...

It often refers to early TV sets that accepted signals from an antenna or VCR only via a coaxial cable. Modern TVs have coax inputs plus inputs that use RCA phono and HDMI cables. See F connector.