Puggo - Jar Jar's Yoda said:

Scope means that each widescreen frame is stretched vertically to fill the entire frame. Then it requires a special lens to stretch it back horizontally when viewing. PG and PSB were scope prints stretched in software after fullscreen capture.

Flat can mean either full frame or widescreen with borders, neither of which require a special lens to project.

Scope is generally the preferred type of 16mm or 8mm print if you're looking for the very best quality.

Then there's the difference between the "Cinemascope" method of squeezing and the "Cineavision" one for 8mm prints.

The Cineavision prints add narrow black bands to the squeezed image to maintain the entire image and not crop it out like the Cinemascope versions do. (As I understand it. Maybe it's the other way around.) I don't know if the actual squeeze ratio is identical, but I suppose it had to be to maintain compatibility with standard anamorphic lenses on projectors.

I have both on my site under the 8mm heading.