3 definitions for R

  RDS : Radio Data System: data sent along with FM radio allowing RDS-compatible tuners to display the names of stations, and other information.

  Receiver : Similar to an amp (you typically wouldn't have a receiver *and* an amp). The difference is that an amp receives an analog signal, and amplifies it for the loudspeakers. A receiver can take any type of signal, analog or digital, decode it (or translate it into 1 or more analog channels) and amplify it for the loudspeakers. Basically, an amplifier is just a volume control. A receiver is a home-cinema amplifier, capable of surround sound in Dolby Digital, DTS or any other format.

  RGB : A video connection, usually through a SCART cable in which 3 color components are carried along separate wires. RGB stands for Red, Green and Blue.