Think about hip and shoulder movement. Both joints can flex, extend, and rotate. Abduction and adduction are also possible. But drop all those terms into your lesson and you'll soon see your students' eyes glaze over. The Fundamental Movements concept can help you guard against this complication because it deals with motion in terms that the students understand, while still being consistent with anatomical and kinesiological nomenclature.
Rotation is rotation-most people understand it.
Most students also know what flexion and extension are or can readily grasp the meaning if you tell them that when pedaling a bicycle they flex one leg as they extend the other. The benefit to the instructor is that he or she does not have to think in instructor language and speak in student language. The benefit to the student is that the instructor will be talking about and teaching things that actually work - movements. After all, students come to us to learn movements that work in snowboarding. The only way they can go home with an understanding of the movements is if we use language that describes these movements and use these movements while riding.