What is the difference between these diana cameras?

All are a type of toy camera. All use 120 film.

Holga- Modern chinese made camera. Available for about $25. Only 1 aperture setting (it has 2 on the camera, but there really is only one), 2 shutter settings, N and B. Hotshoe for flash. Zone focussing lens.

Diana- The original. The camera that started the whole toy camera craze, these were given away as gas station premiums or boardwalk prizes. There are the original vintage Diana cameras ,and then the many clones, which are similar cameras made with many different name plates (Arrow, Windsor, Banner, etc)

3 aperture settings (Usually), 2 shutter settings (Usually, though I've seen many with only 1), The basic model had no flash provision. F models had a flash accessory that used flash bulbs of the ag-1 type.

The Diana F+ by Lomography. $100 (basic Diana+ with no flash, $50)

The flash model version of the Diana+. Otherwise the specs are the same. 4 aperture settings, 1 of which is a pinhole. 2 shutter settings, N and B. Zone focussing lens. The Lomography Diana+ and DianaF+ is unusual in that Lomography has built a system camera out of what was a low tech, low cost camera. You can get 4 interchangeable lenses-35mm, 55mm, and 110mm, fisheye lens and a close up lens attachment as well as a 35mm film back.

Diana Flash: I think you either mean a Diana F or the Diana F+, which are just the Diana camera with a flash attachment.