Or “What is a PCDI?” or “How do I play computer audio through the sound system?”
Does your presentation have any sound effects in it? Video clips? Music? How will attendees hear it? In my experience a lot of folks don’t think about computer audio until the first time they don’t have it.
A direct box (also called DI, or Direct Input Box) is a device used to connect computer audio to a sound system. It transforms the signal into something more easily usable, can remove hum and also protects your equipment. For small breakout rooms you may be able to get by with a set of computer speakers (either bring your own or get them from your AV partner) but for any room where you’re using microphones and have computer audio you’ll also need a direct box.