Sorry.

Puck - What AndrewH described for around $60 is often referred to as a puck since it is about the same size as a hockey puck and is often black.
See link here

Demodulation - probably no product description for a GPS unit will ever mention demodulation but its relevant to the amp/no amp discussion. When the GPS unit receives the satelite signals their frequency is in the gigahertz range like a cell phone. The location information that you are ultimately interested in is encoded in this RF (aka satelite) signal. In order to extract the location info, a process called demodulation occurs.
(this is the same principle as listening to FM radio. When the station broadcasts the show, they modulate the signal. Then when you listen to the show, you have to demodulate to actually hear it)

Amplification / No Amplification - Some GPS systems can amplify the satelite signal before they demodulate it. With an amplified signal you can acquire more satelites which increases the probability that you will always have 3 satelite acquisitions.

But like I said, in the commercial world they might not even have this choice. Don't know...never bought one of these pucks that we're talking about. I just wanted to throw the information out there in case they do.