Different skating techniques for different terrains

Source
http://crosscountryskitechnique.com/skate-skiing/

The 5 primary skate ski techniques, arranged on the power-speed continuum, like gears on a bike or car. (American names in brackets):

1. Diagonal Skate (V Skating)
2. Offset (V1 Skate)
3. One Skate (V2 Skate)
4. Two Skate (V2 Alternate)
5. Free Skate (No Poles)