What is that term to describe the wing motion range?
The term that you are looking for is Wing Flex. The extent of flex is a product of the material.The wing needs a stated definitive strength. With metal, that transforms into a given amount of flex. IOW, the flex, is basically just a by-product of the materials and high aspect ratio design and is not a design goal in itself. The benefit is, smooth ride during a turbulence.

Aerodynamically you do pay a penalty. However, to a certain extent this will be offset by lighter weight and the much superior strength, facilitates the high aspect ratio which more than make up for the loss due to the flex.