What’s “U?”  It’s the major benefit that core listeners derive from the station.  “U” is what the station means to them, what’s expected, and the biggest attribute of listening.  It’s likely the music or some other quality.

Radio listeners are a picky, fickle bunch. They don't listen nearly as much as we would like, have little loyalty to even a favorite personality or station, and are quick to tune out anything that annoys them. It's similar to your loyalty to a "favorite" restaurant. But every radio show can reduce audience turnover by fixing things that drive listeners crazy.