Hearing

As Dr. Sévigny was telling us a little while ago, listening is not hearing. Listening means that you should actually be taking in the information and processing. Hearing is the actual sense that some of us have through our ears. I've posted about listening before, so I decided to look at hearing today.
A good example of hearing would be sitting in driving school and just keeping your eyes open enough to watch the teacher's lips move.
A good example of listening would be actively taking notes during your multimedia lecture because you just realized that the final exam is worth 40% of your final mark.
But what about this: you're sitting in the student centre having lunch and catching up on some philosophy reading when the gaggle of girls sitting next to you start talking about cute guys sitting around them/you pretty loudly. So it distracts you enough that you actually process what they are saying (and eventually look over to who they're talking about...), but you didn't actively sit next to them to listen to their conversation. Would that be hearing the people next to you talk, or would that be listening in on their conversation?
I always wonder, I mean a person can't live with their headphones on for the rest of their lives, although some people look like they do sometimes...
I can't really make up my mind about what it would be: hearing or listening?
What do you think?