FYI - My terminology isn't correct as I'm not a photog, but hopefully I'm somewhat clear and maybe someone else can be more clear than me.
I think they might be talking about the flash trigger. It's something that more professional photographers would use. Instead of having to physically connect the flash to their camera, the camera would fire an infrared pulse (like a remote) or radio singles which would trigger the flashes to flash. That allows you to use multiple flashes at the same time (like they would in a studio).
I can't confirm if Nikon cameras have this though I'd almost guarantee that if they did, then it'd certainly be their higher end D-SLR's and if that's what you're looking at then I'd suggest you do a lot more research.