Spey rods and spey casting have been around for quite a long time. They are said to have been developed in the 1800's in Scotland on the River Spey. They are a two-handed rod and exceptionally long and were evidently developed to make long cast for covering a lot of water (common in salmon and steelhead fishing). Another reason for their design was the fact that many of the Scottish salmon rivers are lined with trees and brush making a traditional backcast very difficult.
Spey rods are typically from 12-14 feet in length and they can be either single-handed or double-handed. The double-handed rods are more traditional and more common.
I do have some limited experience with a spey rod. I can tell you this from personal knowledge...a proper spey cast is basically a long and graceful and somewhat confusing looking roll cast. With these very long rods, not only can you make longer cast, you can also mend a lot of line...both are just what you need when covering a lot of water is called for salmon/steelhead fishing.
Here is more information on spey rods and spey casting:
Here is a downloadable pdf that is very well written - see here...
Spey Casting - Roll And Switch Casting (video - Orvis/Pete Kutzer)