It's a way of having the radio find the type of station you like to listen to. Must not of made it, tho, because it seems to be on '02's only - I have an '02 Grand Marquis with the function, so I looked-it-up. When you push the RDS button, there should pop-up a list of different kinds of stations, like talk, light rock, country, etc. You pick the one you want, & the radio will automatically look for stations that have the RDS system & advertise that style. Also, some of the stations transmit the name of the song that's playing, & that shows up, too.