If you're in a meeting with smart people and they start discussing a term or concept you don't understand, what do you do?
Do you know what recombinant DNA is? Analytics? Chapter 7? Fair use? RSS? The Long Tail?
If smart people in your industry are talking about an issue you don't know cold, it's very important that you don't just sit there and nod your head sagely. I think there are two constructive paths. The first is to ask. "Wait, I was with you until a second ago. What does that mean?" You'll be amazed at how smart and engaging this makes you seem if you say it at the right time.
The second approach is to write it down and not go to bed that night until you know the topic better than the person who brought it up. How else, precisely, are you going to become one of the smart people?