What does RCA stands for when referring to audio cables?

RCA is an electronics company, just like Sony or Toshiba. (RCA stands for "Radio Corporation of America.") RCA formed in 1919 and was in existence until 1986. Currently the trademark of RCA is used by Sony Music Entertainment.

also

An RCA connector, sometimes called a phono connector or cinch connector, is a type of electrical connector commonly used to carry audio and video signals. The name "RCA" derives from the Radio Corporation of America, which introduced the design by the early 1940s for internal connection of the pickup to the chassis in home radio-phonograph consoles. It was originally a low-cost, simple design, intended only for mating and disconnection when servicing the console.