The RCA connector was developed in the 40's and has been used since as a low cost, simple alternative to the larger 1/4" connector. It's name is derived from the Radio Corporation of America. It was known as a "phono connector" or "cinch connector" but has been replaced simply by the term "RCA plug". Now used in nearly all but the highest-end consumer audio and video products you will find they are commonly used on audio/video devices and are called "A/V plugs or jacks" because of this.