Unlike trout fly fishing, there are 3 Designs of Spey Casting, each with there own techniques, advocates and critics. Anybody wanting to enter into Spey casting with two-handed rods can get bombarded by ideas and terms that can be overwelming.
This video belongs to a series that sets out to streamline as much as possible, the world of Spey casting. Especially it takes a look at the 3 kinds of line systems and relates them to the methods which they are cast. Each casting design looks for to make use of the attributes of the line for simple casting and fishing.
Clearly this video does not cover whatever there is to state about the topic, however it is a helpful generalization on the casting distinctions in between the designs and why they exist.