You get into an elevator and there's music playing. You hear it, but you're not into it. That is passive.
The television set's on while the family's sitting around having dinner or talking. Nobody's watching TV; it's there; they're aware of it, but they're not participating. That's passive.
You're in the car, you're talking to somebody, the radio's on, music's playing, you're not really listening to it; you're aware of it; that's passive.