Each radio station gets a single frequency, which you tune into. But they aren’t actually just given a single frequency: they get all the nearby frequencies too. So for instance if you tune into 106.2, the broadcaster can actually use everything from 106.17 to 106.23. They put the music on one frequency — say, 106.20 — but they can use other frequencies for other things. So 106.17 carries the song title, artist, and so forth, 106.21 has a stereo track that the radio only cares about if you have surround sound, etc.
It’s a tech called Radio [Data System (RDS)](https://en.wikipedia.org/wiki/Radio_Data_System).
Basically, there’s some room in FM broadcast signals for things other than 20Hz-20kHz audio, so RDS was conceived as a standard for transmitting some simple text in a specific portion of that unused bandwidth.
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