Radio Corporation of America
RCA is a kind of plug created by this company, which is largely used by sound systems, TV sets, VCRs, camcorders, etc. They are used for both audio and video connection (“video in” and “video out” plugs found on your VCR use this kind of connector).
On the PC RCA plugs are normally associated to composite video connection – the same kind of video signal used by the “video in” input located on your TV set or VCR and “video out” output located on your VCR. Only video card with “TV out” or “VIVO” function have a female RCA plug to allow you to connect your computer to your TV set or VCR. Sometimes the video card only provides a S-Video output, which can be converted into a RCA plug thru the use of an adaptor.
Professional or external sound cards also use this kind of plug since tape decks, receivers, etc use RCA plugs and not mini jacks (which is the kind of plug normally found on regular sound cards).
Digital audio connection, called SPDIF, also use this kind of plug.

Figure 1: Male RCA plugs.

Figure 2: Female RCA plugs.